EXPERIMENTAL 
-WIRELESS 
STATIONS 

THEIR 

THEORY,  DESIGN,  CONSTRUCTION 
AND  OPERATION 

INCLUDING     WIRELESS     TELEPHONY     AND 
QUENCHED  SPARK  SYSTEMS. 

A  complete  account  of  sharply  tuned  modern  wireless 

installations  for  experimental  purposes  which 

comply  with  the  new  wireless  law,  with 

more  than  80  illustrations. 

By 
PHILIP  E.  EDELMAN 

t  t 

Author,  "Inventions  and  Patents,"  "Simple  Experiments 

in  Chemistry,"  "An  Experimental  Quenched  Arc 

System,"  "How  to  Comply  with  the  New 

Wireless  Law,"  and  many  other 

articles  in  the  technical 

press. 


THIRD  REVISED  EDITION 

Fourth  Printing. 

Published  by  die  '*$&?• 
MINNEAPOLIS,  MINN.,  U.  3.  A.    *• 

1915          ...    .      -    .     . 


Copyright,  1912-4 

by 

PHILIP  E.  EDELMAN,  MINNEAPOLIS,  MINN. 
All  rights  reserved,  including  translations. 


FIRST  EDITION  PUBLISHED  NOVEMBER,  1912. 


BOOKS  BY  PHILIP  E.  EDELMAN. 

(Now  ready,  or  in  preparation.) 

"Experimental  Wireless  Stations"     .      .      .      .     $1.50 

"Experiments"  A  book  which  takes  the  reader  into  the 
very  inside  of  experimenting,  electricity,  wireless, high 
frequency,  chemistry  and  physics  .  .  .  .  $1.50 

"How  to  Make  and  Use  a  Wireless  Station"  Complete 
instructions  for  an  inexpensive  set  that  complies  with 
the  law 12c 

"Inventions  and  Patents"  A  book  for  inventors  and  all 
who  are  concerned  with  patent  rights  .  .  .  $1.00 

"Applied  Radio  communication"  A  work  which  covers 
the  commercial  side  of  wireless  telegraphy,  telephony, 
and  control  as  thoroughly  as  this  volume  covers  the 
experimental  field. 

"Small  Transformers"  A  working  manual  showing  how 
to  make  £.11  sizes  cf  small  transformers  for  radio,  high 
frequency,  shop,  arid  laboratory  purposes. 


the  faculty  of  the  West  High  School,  Minneapolis, 

and  particularly  to  Mr.  John  H.  Cook  of  the 

Physics  Department,  as  an  appreciation 

of  the  interest  taken  in  the 

Author. 


343115 


FOREWORD. 


This  book  was  written  to  fill  a  noticeable  gap  in  the 
literature  on  the  art  of  wireless  telegraphy.  As  its  name 
implies  it  is  intended  particularly  for  experimenters,  that 
sane  body  of  voluntary  workers  who  take  up  the  art  as  a 
hobby,  study,  or  spare  time  vocation  and  who  are  gener- 
ally misnamed,  "amateurs."  It  is  intended  particularly  as 
a  guide  to  a  rational  worth  while  study  of  the  art  and  only 
matter  which  directly  contributes  to  the  practical  presenta- 
tion of  the  art  has  been  included. 

One  of  the  main  objects  of  the  book  is  to  provide  a 
standard  design  for  so-called  "Amateur  stations,"  which 
will  take  the  place  of  the  many  varieties  of  hit  and  miss 
apparatus  constructed  and  purchased  by  experimenters. 

This  book  is  intended  for  experimenters  who  regard 
the  art  as  more  than  a  mere  idle  plaything,  and  it  is  hoped 
that  it  will  serve  as  a  stepping  stone  to  a  serious  prepara- 
tion for  high  positions  in  the  practical  field  of  the  art. 
The  earnest  experimenter  is  separated  from  the  wireless 
engineer  and  commercial  wireless  inventor  by  a  very 
small  space  of  time  and  application  to  study,  while  the 
position  of  an  expert  wireless  operator  is  even  easier  to 
attain.  Wireless  today  offers  opportunities  which  are 
perhaps  not  exceeded  by  any  other  art  or  trade.  The 
field  is  open  and  ready  for  serious  workers,  the  work  of 
absorbing  interest,  and  the  remuneration  limited  only  by 
the  capabilities  and  temperament  of  the  individual  and  the 
circumstances  concerned. 


Experimental  Wireless  Stations. 


Inasmuch  as  both  innocent  and  wilfull  interference 
with  other  stations  has  to  a  large  extent  hindered  experi- 
menters as  well  as  commercial  operators,  the  design  in 
this  book  is  directed  particularly  to  standard  apparatus 
and  stations  of  sane  sharp  tuned  wave  lengths  which  will 
not  interfere  with  others.  As  far  as  the  author  is  aware 
this  is  the  first  book  to  appear  in  which  standard  designs 
are  given.  On  account  of  the  new  wireless  law,  experi- 
menters are  now  forcefully  restricted  to  this  rational  type 
of  apparatus.  In  any  case,  serious  workers  will  realize 
that  it  is  only  fair  and  even  desirable.  At  the  present 
stage  of  development,  wireless  experiments  must  be  con- 
ducted on  a  strict  basis  of  live  and  let  live. 

The  matter  in  this  book  has  been  written  with  particu- 
lar regard  to  clearness,  simplicity,  and  direct  use  fullness. 
Makeshifts  have  been  suggested  in  some  cases  and  it  is 
hoped  that  experimenters  with  limited  means  will  wel- 
come them.  It  is  quite  possible  to  have  a  wireless  station 
at  an  outlay  of  less  than  one  dollar.  The  approximate 
cost  of  the  apparatus  is  given  in  some  cases. 

The  author  will  be  pleased  to  receive  suggestions  and 
corrections  from  his  readers,  but  cannot  promise  or  agree 
to  give  individual  advice,  further  individual  instructions, 
or  answer  other  communications  which  require  much  time, 
since  his  time  is  all  taken  up  with  other  activities. 

In  order  to  get  directly  to  the  pith  of  the  subject  little 
or  no  preparatory  history  and  elementary  matter  has  been 
given,  as  the  readers  are  assumed  to  have  some  little 
knowledge  of  the  fundamentals  of  electricity,  magnetism, 
and  mathematics.  (This  does  not  mean  an  extensive  or 
complete  knowledge.)  The  important  principles  upon 
which  the  wireless  systems  depend  together  with  the 
working  principles  of  the  separate  instruments  have,  how- 
ever, been  treated  in  some  detail  and  in  most  cases  "How 


Foreword. 


it  works  and  how  to  make  it,"  have  been  combined.  It  is 
believed  that  several  items  are  presented  for  the  first  time 
in  this  volume  and  the  best  modern  practice  has  been  pre- 
sented, so  that  it  comes  within  the  limitations  of  the  aver- 
age experimenter. 

The  majority  of  the  material  given  is  the  result  of  the 
author's  own  experiences  together  with  the  experiences 
of  others,  and  it  is  believed  that  credit  has  been  given  for 
the  important  items  or  abridgements  from  other  sources, 
which  have  been  included.  In  many  cases  only  the  vital 
points  for  an  instrument  have  been  given,  so  that  the  indi- 
vidual can  use  his  own  ingenuity  in  working  out  the  de- 
tails. The  reader  is  thus  given  an  opportunity  to  be  orig- 
inal without  the  usual  waste  of  "cut  and  try."  Every  am- 
bitious reader  will  very  likely  read  from  cover  to  cover, 
but  the  matter  has  been  so  arranged  that  each  chapter  is 
complete  in  itself.  The  advanced  reader  can  turn  to  the 
particular  subject  in  which  he  is  interested  without  going 
through  matter  already  familiar  to  him. 

Although  several  manufacturers  have  offered  cuts  for 
this  book,  it  has  seemed  best  to  give  simple  line  drawings 
to  illustrate  constructional  details  rather  than  half  tones 
which  only  show  the  general  appearance  of  a  particular 
type  of  instrument.  Most  of  the  drawings  have  been  pre- 
pared specially  for  this  book  and  the  few  taken  from 
other  sources  have  in  most  cases  been  credited. 

In  conclusion  it  may  be  remarked  that  no  author  is  in- 
sensible to  appreciation,  and  if  you  obtain  more  than  the 
mere  intrinsic  worth  from  this  book,  the  author  will  ap- 
preciate your  courtesy  in  telling  others  so. 


Philip  E.  Edelman. 


Minneapolis,  Minnesota, 
October  15,  1912. 


CHAPTER  I. 


NATURE  AND  THEORY  OF  WIRELESS  TRANS- 
MISSION OF  INTELLIGENCE. 

Before  beginning  the  details  of  equipment,  a  brief  out- 
line of  the  essential  theories  which  aid  in  understanding 
the  art  will  be  given.  To  begin  with,  it  should  be  under- 
stood that  many  of  the  elementary  theories  have  only  been 
partially  substantiated  and  that  in  any  case  they  serve 
more  for  convenience  than  as  scientific  fact.  It  should 


\ 
C 

\ 

7A*                        A-V 

c' 

PI 

is 

* 
< 

^i                                       rstnFi 

8                                                      ]  gj.PYn 

T 

"*^^ 

i 

j 

- 

FIG.  1. 

A.  Al — aerials.  C.  Cl — condensers.  T — transformer  or  coil. 
D.— detector.  I.  II — inductances.  S — Spark  gap. — G. — ground. 
R. — telephone  receiver. 

also  be  remembered,  that  while  lines  of  force  and  similar 
terms  are  used  as  though  the  lines  were  visible  and  a  mat- 
ter of  fact,  they  are  merely  imaginary  and  used  for  con- 
venience. 

In  the  practical  wireless  station  with  which  we  are 
concerned,  electromagnetic  waves  are  utilized  to  transmit 
intelligence  in  a  telegraph  code  without  the  use  of  a  con- 
ductor or  wire  between  the  transmitting  and  receiving  sta- 


Theories  of  Transmission. 


tions.  It  has  been  found  that  these  electromagnetic  waves 
closely  resemble  light  waves  and  for  this  reason  some 
knowledge  of  the  physics  of  light  will  be  useful  and  an 
aid  in  the  mastery  of  the  wireless  art. 

In  fig.  1  a  simple  diagram  of  the  relations  of  the  sta- 
tions is  shown.  Briefly,  electromagnetic  waves  are  gen- 
erated by  means  of  a  discharge  through  a  suitable  gap 
which  sets  up  oscillations  in  a  shunt  circuit  of  capacity  and 
inductance  and  these  oscillations  are  in  turn  radiated  from 
the  aerial  in  wave  trains  representing  the  dots  and  dashes 


//////////////////////////////// 

FIC.   I^.  THEORY  OF  THE   ACTION   OF     WIRELESS    WAVES 


of  the  code.  By  referring  to  the  figure  it  will  be  observed 
that  the  sending  and  the  receiving  station  are  connected 
through  the  earth  and  that  they  have  a  second  circuit 
through  the  space  between  their  respective  aerial  capaci- 
ties. It  has  not  been  established  whether  the  ground  acts 
as  the  return  circuit  or  whether  the  space  serves  for  this 
purpose,  but  experiments  have  shown  that  a  considerable 
part  of  the  efficiency  of  transmission  is  dependent  on  hav- 
ing good  ground  connections  through  soil,  which  is  a  com- 
paratively good  conductor.  In  fact,  the  variable  conduc- 
tivity over  different  portions  of  the  earth  materially  af- 
fects the  range  and  clearness  of  transmission,  ranging 
from  maximum  over  water,  to  a  minimum  over  dry  un- 


10 


Experimental  Wireless  Stations. 


even  expanses  of  land.  The  earth  is  an  imperfect  and 
variable  conductor  in  itself  and  it  is  for  this  reason  that 
transmission  over  different  portions  of  the  earth's  surface 
varies  considerably.  It  has  not  been  established  whether 
or  not  the  curvature  of  the  earth  materially  affects  trans- 
mission, but  it  is  not  likely  that  it  does.  Good  earth  con- 
nections then,  are  essential  to  efficient  wireless  transmis- 
sion. 

A  commonly  accepted  theory  of  the  action  of  wireless 
waves  is  illustrated  in  fig.  1  a.  The  aerial  (A)  is  repre- 
sented by  the  upper  part  of  a  spark  gap  and  the  lower 
part  terminates  in  a  ground  E.  The  aerial  becomes 


:5|A' 

n 


charged  and  sets  up  a  field  of  force,  the  area  of  which  de- 
pends on  the  intensity  of  the  charge  and  other  natural 
conditions.  The  lines  of  electrical  strain  are  represented 
by  the  dotted  lines  and  should  be  understood  as  of  spheri- 
cal form,  although  shown  as  in  a  plane  on  the  paper.  Now 
after  the  charge  accumulates  to  a  certain  point,  a  spark 
passes  between  the  gap  electrodes,  making  the  gap  a  tem- 
porary conductor.  The  aerial  discharges  at  this  point  and 
as  a  result  the  strain  in  the  electrostatic  field  is  relieved. 
However,  a  new  current  is  simultaneously  produced  which 
charges  the  aerial  in  substantially  the  opposite  polarity  to 


Theories  of  Transmission.  11 

that  of  the  first  charge,  and  the  process  is  repeated  very 
rapidly  a  number  of  times.  That  is,  the  aerial  is  said  to 
oscillate  or  vibrate.  Now,  each  reversal  of  the  polarity  of 
the  charge  causes  the  direction  of  the  strain  to  change  so 
that  the  lines  resulting  from  the  first  charge  are  displaced 
by  lines  running  in  the  opposite  direction,  thus  forming 
partial  loops.  These  loops  form  a  circular  series  of  rip- 
ples or  waves  about  the  aerial  and  travel  away  from  it  at 
the  rate  of  300,000,000  meters  per  second  (186,000  miles 
per  second),  or  the  speed  of  light.  In  the  figure,  the  ar- 
rows represent  the  direction  of  the  lines  of  strain  and  a 
little  study  of  this  imaginary  diagram  will  aid  in  the  un- 
derstanding of  wireless  phenomena.  It  is  understood,  of 
course,  that  the  gap  is  charged  by  a  suitable  condenser  and 
source  of  power,  which  are  not  shown. 

Two  complete  oscillations  are  represented  by  the  loops 
of  fig.  la.  and  the  aerial  is  ready  for  a  third  discharge. 


Stratq. 


•I]  \  •::'.•' 


1H  IS' 

Jsigijt         -.-— i— - 

T7       TA> 


G. 

FIG.  3. 


RE. 


These  oscillations  really  occur  at  an  exceedingly  rapid 
rate  and  has  already  been  explained,  the  lines  are  only 
imagined  to  exist  for  the  sake  of  tangible  theoretical  con- 
sideration. 

The  function  of  the  aerial  capacities  of  the  stations 


12  Experimental  Wireless  Stations. 

will  be  best  understood  perhaps,  when  they  are  likened  to 
a  simple  condenser.  (See  fig.  2.)  If  this  theory  is  ac- 
cepted, a  wireless  circuit  is  practically  a  closed  circuit  in 
which  one  branch  takes  the  form  of  a  condenser.  How- 
ever, since  the  distance  between  the  two  aerials  concerned 
is  generally  many  miles,  it  is  not  unlikely  that  the  effect 
is  similar  to  that  indicated  by  fig.  3,  since  it  has  been  estab- 
lished that  the  upper  strata  of  the  atmosphere  and  the  sur- 
rounding space  form  practically  a  perfect  conductor.  At 
any  rate,  the  distance  to  which  transmission  may  be  car- 
ried out  is  less  with  relatively  low  aerials  than  with  high 
ones,  the  other  conditions  remaining  the  same,  and  for 
this  reason  the  higher  the  aerial  can  be  supported,  the  bet- 
ter. The  item  of  cost  is  the  practical  limit,  however, 
since  after  a  moderate  height  is  reached  the  expense  in- 
creases in  a  proportion  many  times  greater  than  the  corre- 
sponding increase  in  height.  In  fact,  the  height  of  ex- 
perimental aerials  will  naturally  be  limited  for  this  reason 
and  even  in  the  few  large  commercial  stations,  tho.  aerial 
supports  form  one  of  the  largest  items  of  expense. 

Now  the  transmitted  wave  impulses  do  not  travel  only 
in  the  desired  direction  to  the  receiving  station,  but  spread 
out  in  all  directions  with  practically  equal  force.  The 
direction  of  transmission  can  be  regulated  to  some  extent, 
however,  by  means  of  directive  aerials  which  tend  to 
make  the  range  of  transmission  greater  in  one  desired 
direction  than  in  other  directions.  Wireless  transmission 
is  perhaps  best  understood  by  a  comparison  to  the  waves 
which  result  when  a  small  stone  is  thrown  into  a  smooth 
body  of  water.  It  is  suggested  that  the  reader  try  the 
experiment  when  the  opportunity  is  presented,  if  he  has 
not  already  done  so.  The  stone  thrown  into  the  water 
corresponds  to  the  wave  generator  at  the  transmitting 
station  in  wireless  telegraphy,  the  water  to  the  space  or 


Theories  of  Transmission.  13 

ether  and  the  ripples  to  the  electromagnetic  waves.  It 
should  be  observed  that  the  ripples  spread  out  contin- 
ually in  the  form  of  a  circle  and  that  they  gradually  be- 
come feeble  and  feebler,  until  they  are  no  longer  visible. 
Wireless  transmission  presents  a  similar  property  and  the 
electromagnetic  waves  become  feebler  so  that  the  ampli- 
tude is  approximately  inversely  proportional  to  the  dis- 
tance from  the  sending  station.*  Another  factor  which 
limits  the  transmitter's  effective  range  is  the  item  of  ab- 
sorbtion.  Now,  it  has  been  found  that  the  absorbtion 
varies  in  some  cases  with  the  wave  length  employed.  In 
general,  long  wave  lengths  are  subjected  to  less  absorption 
than  wave  lengths  which  are  relatively  short.  Inasmuch 
as  the  experimenter  is  expected  to  confine  his  experiments 
to  the  use  of  short  wave  lengths  this  is  a  matter  of  some 
importance.  In  transmission  over  water  short  wave 
lengths  are  nearly  as  good  as  the  long  ones,  but  over  ordi- 
nary land,  long  wave  lengths  are  a  material  advantage. 
However  in  the  case  of  land  transmission  over  dry  soil, 
neither  long  nor  short  wave  lengths  appear  to  have  an 
advantage.  It  is  understood  that  short  waves  mean  those 
having  a  wave  length  of  200  meters  or  less,  while  long 
waves  refer  to  waves  having  from  1,200  to  4,000  or  more 
meters  for  their  wave  length.  Wave  lengths  between  300 
and  600  meters  are  generally  recognized  as  the  most  ad- 
vantageous for  ordinary  purposes  and  since  they  are  used 
for  commercial  purposes  the  experimenter  is  expected  to 
use  wave  lengths  which  do  not  come  within  this  range  to- 
gether with  a  safe  margin,  in  order  to  avoid  needless  and 
useless  confusion. 

Other  items  which  affect  the  transmission  are  irregu- 
larities in  the  composition  of  the  earth  such  as  mountains, 


This  is  not  a  rigid  rule  or  even  exact. 


14  Experimental  Wireless  Stations. 

minerals,  etc.,  and  daylight.  It  has  been  found  that  mes- 
sages can  be  received  over  much  greater  distances  at  night 
than  during  the  daytime.  The  difference  is  not  marked 
or  important  over  short  distances  and  can  be  overcome  to 
a  considerable  extent  over  long  distances,  by  the  use  of 
long  wave  lengths.  The  reason  why  daylight  affects  the 
transmission  is  not  really  understood  at  the  present  time, 
although  there  are  several  theories.  It  is  believed  that 
the  effect  is  due  either  to  the  ionization  of  the  air  or  the 
upper  strata  or  both,  by  the  sun's  light.  When  the  theory 
that  the  aerial  capacities  of  the  stations  form  a  condenser 
is  used  and  it  is  remembered  that  the  action  of  a  condenser 
depends  largely  upon  having  a  good  dielectric  material  so 
that  there  will  be  little  leakage,  this  theory  seems  plaus- 
ible. Rain  and  damp  weather  have  a  similar  effect  on 
transmission  because  the  dielectric  is  presumably  rendered 
less  conductive  to  the  waves  and  more  conductive  to 
leakage. 

Now  since  the  waves  tend  to  spread  out  in  all  direc- 
tions, it  will  be  evident  that  all  the  receiving  stations  with- 
in the  range  of  a  transmitting  station  will  be  capable  of  re- 
ceiving the  same  message  equally  well,  other  conditions 
remaining  the  same.  This  lack  of  secrecy  is  a  consider- 
able detriment  to  the  advance  of  the  art  and  efforts  are 
constantly  being  made  to  overcome  this  lack  of  direct 
communication  in  a  desired  straight  line.  Instruments  and 
apparatus  have  been  developed  which  make  it  possible  to 
either  receive  or  not  receive  a  given  message  with  a  cer- 
tain degree  of  precision  and  directive  methods  have  been 
developed  to  a  certain  degree  as  has  already  been  men- 
tioned. Another  serious  drawback  to  the  advancement  of 
the  art  is  the  matter  of  interference.  This  is  an  item 
which  directly  concerns  the  experimenter  and  although 
several  arrangements  to  overcome  this  objectionable  fea- 


Theories  of  Transmission.  15 

ture  have  been  developed,  there  is  considerable  room  for 
improvements. 

Interference  can  be  understood  by  reference  to  the  ex- 
periment of  throwing  the  stone  into  the  water.  If  two 
stones  instead  of  one  are  thrown  into  the  water, and  if  one 
is  considerably  larger  than  the  other,  it  will  be  noticed  that 
the  ripples  or  waves  from  the  larger  stone  tend  to  absorb 
and  superpose  those  of  the  smaller  stone.  A  similar 
drowning  out  occurs  in  wireless  transmission,  and  when 
several  stations  are  sending  simultaneously  it  becomes 
practically  impossible  to  select  a  desired  message  unless 
it  is  noticeably  stronger  than  the  remainder  of  the  im- 
pulses. It  frequently  happens  that  six  or  more  stations 
are  sending  simultaneously  with  approximately  the  same 
wave  length  and  with  strong  apparatus,  making  it  nearly 
impossible  to  receive  an  intelligible  message  from  a  single 
one  of  them.  Further,  when  a  long  distance  message  is 
being  received,  and  another  station  sending  at  approxi- 
mately the  same  wave  length  and  situated  in  the  neighbor- 
hood of  the  receiving  station  starts  in,  the  result  is  ob- 
vious. To  be  sure,  apparatus  has  been  developed  which 
makes  the  selection  of  desired  signals,  to  the  exclusion  of 
others,  certain  within  limits,  but  such  cases  as  the  one 
mentioned  can  of  course  not  be  entirely  avoided,  with 
the  best  of  the  present  apparatus.  When  the  stations  are 
all  sending  at  wave  lengths,  which  differs  considerably 
from  one  another  and  are  sharply  tuned,  the  desired  mes- 
sage can  generally  be  received  without  much  difficulty. 
However,  if  untuned  or  only  loosely  tuned  signals  are  sent 
out  from  a  moderately  strong  or  neighboring  station,  it 
becomes  practically  impossible  to  tune  them  out  because 
they  are  received  by  forced  oscillations.  It  is  like  trying 
to  hear  a  phonograph  a  block  away  when  a  band  is  play- 
ing within  a  few  feet  of  your  ears. 


16  Experimental  Wireless  Stations. 

When  tuned  or  sharply  tuned  waves  are  spoken  of,  it 
means  waves  such  as  are  transmitted  from  tuned  trans- 
mitting stations  so  that  it  is  necessary  to  tune  within  a 
very  few  per  cent  in  order  to  receive  them.  When  un- 
tuned or  forced  oscillations  are  spoken  of,  it  means  waves 
which  may  be  received  without  sharp  tuning  or  signals 
which  have  several  wave  lengths  without  any  definite 
characteristics.  This  is  the  sort  which  is  so  generally  em- 
ployed by  beginners  and  even  by  commercial  stations  in 
some  cases  and  can  be  received  by  all  stations  within 
range  without  any  special  effort.  This  property  is  cer- 
tainly useful  in  case  of  emergencies  at  sea,  but  in  ordi- 
nary transmission  the  stations  with  untuned  wave  trans- 
mission are  like  noxious  weeds,  and  should  be  gotten  rid 
of  as  soon  as  possible  whenever  they  interfere  with  other 
stations.  The  matter  of  tuning  will  be  more  fully  taken 
up,  later. 

The  only  other  natural  condition  of  importance  which 
affects  wireless  transmission  is  the  matter  of  atmospheric 
disturbances.  Ordinary  static  disturbances  resenible  the 
disturbances  caused  by  untuned  waves  and  are  practi- 
cally impossible  to  entirely  exclude,  particularly  when 
they  are  present  in  a  large  quantity.  Certain  localities 
have  less  trouble  from  static  interferences  than  others, 
but  there  are  only  a  few  localities  in  which  static  does 
not  cause  more  or  less  trouble.  In  cases  of  local  elec- 
trical storms,  transmission  or  reception  becomes  imprac- 
ticable and  even  dangerous. 

The  sending  and  the  receiving  stations  of  a  wireless 
system  are  similar  and  the  same  aerial  capacity  may  be 
used  for  both  sending  and  receiving.  The  receiving  ap- 
paratus of  an  up-to-date  wireless  system  generally  in- 
cludes a  detector  to  detect  or  rectify  the  incoming  os- 
cillations, sensitive  recorders,  which  generally  take  the 


Theories  of  Transmission.  17 

form  of  telephone  receivers,  to  receive  the  intelligence, 
and  various  inductive  and  capacity  apparatus  to  tune 
the  station  to  receive  desired  signals  to  the  exclusion  of 
undesired  signals. 

These  points  and  the  practical  considerations  which 
they  involve  will  be  discussed  in  detail  in  the  following 
chapters. 

The  reader  should  always  bear  in  mind  that  the  radiant 
energy  used  for  wireless  work  is  as  real  as  is  the  radiant 
energy  of  the  sun.  The  length  of  the  electric  waves  with 
which  we  are  concerned  can  be  controlled  at  will  and 
while  they  may  be  made  a  fraction  of  an  inch  or  several 
miles  long  by  merely  altering  the  oscillatory  cir;uit  as 
described  in  chapter  four,  practical  work  is  at  present 
carried  out  within  150  to  6,000  meters. 

The  matter  in  this  chapter  is  only  a  mere  outlitre  of 
the  many  conditions  involved  in  wireless  transmission, 
and  the  reader  is  referred  to  works  by  Pierce,  Fleming, 
Murray,  and  others,  for  further  accounts  of  the  history 
and  theories  of  wireless  transmission.  The  mathematical 
reader  will  find  these  volumes  of  particular  interest. 


CHAPTER  II. 


AERIALS. 

The  essential  conditions  for  wireless  transmission  have 
been  briefly  outlined  and  we  will  now  take  up  the  matter 
of  aerials.  It  will  be  remembered  that  short  waves  are 
more  easily  dissipated  than  long  waves.  This  is  particu- 
larly true  during  the  summer  months  and  when  the  trans- 
mitting station  is  in  the  vicinity  of  a  large  number  of 
trees.  Both  the  sunlight,  and  the  foliage  on  the  trees 
tend  to  absorb  the  shorter  waves  to  a  greater  extent 
than  the  longer  waves.  Perhaps  it  is  well  to  more  fully 
define  what  is  meant  by  wave  length  at  this  time. 

Now  the  electromagnetic  waves  which  are  generated 
and  radiated  at  the  sending  station  are  similar  to  light 
waves  in  that  they  have  the  same  velocity  (186,000  miles 
per  second)  in  air  of  the  same  temperature  and  pressure, 
have  the  physical  properties  of  reflection,  refraction  and 
polarization,  but  are  different  in  that  light  waves  have  a 
relatively  short  wave  length  while  the  electrical  oscilla- 
tions have  a  relatively  long  wave  length.  It  may  be  ex- 
plained also,  that  the  length  of  a  wave  means  the  distance 
between  like  points  on  any  two  consecutive  waves.  It 
will  be  remembered  and  noted  that  the  transmitter  of  a 
wireless  station  sends  out  a  series  of  waves  at  a  very 
rapid  rate,  so  that  by  the  time  one  has  left  the  aerial  and 
another  leaves,  the  first  will  have  traveled  a  distance 
roughly  equal  to  the  wave  length.  Since  these  wave  im- 


Design  for  Aerials.  19 

pulses  occur  at  a  very  rapid  rate  (high  frequency),  a 
single  transmitted  dot  may  be  made  up  of  several  wave 
impulses. 

The  aerial  capacity  or  antenna  consists  of  metallic 
conductors  insulated  from  foreign  objects  and  elevated 
in  the  air.  It  is  generally  made  up  of  a  number  of  sim- 
ilar wires,  and  its  purpose  is  to  radiate  electromagnetic 
waves  when  used  as  the  aerial  for  a  transmitter,  and  to 
receive  or  regenerate  intercepted  waves  when  used  with 
receiving  apparatus.  The  aerial  itself  may  take  a  number 
of  shapes  and  since  each  has  individual  characteristics, 
different  effects  are  obtainable  from  different  combina- 
tions of  conductors.  In  the  early  stages  of  the  art  solid 
metal  or  wire  network  aerials  were  adopted  and  the  ex- 
perimenters used  chicken  netting,  bronze  screen  and  sim- 
ilar materials  for  aerials,  but  it  was  soon  found  that 
uniform  conductors  separated  by  a  uniform  distance  were 
better  suited  for  this  purpose. 

Now  the  dimensions  of  the  aerial  is  one  of  the  main 
factors  which  determine  the  efficiency  of  the  wireless  sta- 
tion and  also  limit  the  efficient  wave  length  of  the  trans- 
mitted impulses.  In  accordance  with  good  practice  and 
in  order  to  keep  within  the  regulations  embodied  in  pend- 
ing wireless  legislation,*  the  experimenter  is  expected  and 
will  very  likely  be  required  to  limit  his  experiments  to 
wave  lengths  which  are  not  over  two  hundred  meters 
long,  or  else  to  use  wave  lengths  of  a  very  long  length, 
(2,000  meters  or  more) .  Now  although  low  wave  lengths 
are  more  readily  absorbed  and  dissipated  they  are  also 
more  suited  to  low  power  apparatus  than  the  long  wave 
lengths.  However,  if  the  reader  proposes  to  use  power  in 
excess  of  one  K.  W.,  it  will  be  advisable  to  use  the  long 
waves  for  the  experiments  in  order  to  obtain  a  desired 


20  Experimental  Wireless  Stations. 

degree  of  efficiency.* 

When  the  experiments  are  to  be  carried  out  in  the 
vicinity  of  considerable  foliage  it  will  be  advisable  per- 
haps, to  use  the  long  wave  length,  but  in  all  ordinary  con- 
ditions and  particularly  in  cities  having  numbers  of  other 
stations,  the  short  wave  length  only  should  be  used.  It 
should  be  remembered  that  the  aerial  itself  is  only  one 
of  the  factors  which  determine  the  transmitted  wave 
length  and  that  the  experimenter  has  a  variable  range 
of  wave  lengths  at  his  service  by  employing  tuning  helixes, 
oscillation  transformers,  or  if  very  high  wave  lengths  are 
desired  he  may  use  a  loading  coil. 

The  first  item  to  consider  is  the  exact  location  for  the 
aerial  support,  or  the  support  and  the  height  for  the  same. 
As  has  already  been  pointed  out,  the  higher  the  aerial  is 
placed  above  the  surface  of  the  earth,  the  better.  When 
only  occasional  experiments  are  to  be  conducted,  a  tandem 
of  kites,  preferably  box  kites,  will  serve  very  well.  The 
unsteady  height  resulting  from  the  rising  and  falling 
motion  is,  however,  not  suited  to  delicate  tuning,  since  the 
capacity  of  the  aerial  is  thereby  altered.  There  is  no 
limit  to  the  ingenuity  which  may  be  called  to  act  in  the 
selection  of  inexpensive  aerial  supports.  A  simple  insul- 
ated wire  dropped  from  the  roof  or  an  upper  story  of  an 
apartment  house,  flat,  water  tower,  or  similar  structure  to 
a  position  some  distance  below  (30  to  130  feet),  will  serve 
as  a  fair  aerial.  Insulated  telephone  cables  may  be  im- 
pressed into  service  for  receiving  purposes  alone.  Two 
grounds  may  be  used  in  place  of  an  aerial,  if  no  supports 
are  available.  Thus  the  water  pipes  may  be  used  as  an 


*  See  Chapter  19.    The  law  referred  to  has  been  en- 
acted. 


Design  for  Aerials.  21 

aerial  while  the  gas  pipes,  or  a  cistern  is  used  as  the 
ground.  Or  the  steel  frame  or  tin  roof  of  a  building  may 
be  used  for  an  aerial  while  another  part  of  another  build- 
ing is  used  for  a  ground.  Even  leader  pipes  and  gutters 
have  been  impressed  into  service  in  certain  cases.  Com- 
mon wire  netting  suspended  from  trees  or  telephone  poles 
may  be  utilized.  It  is  always  desirable  to  insulate  even 
makeshift  aerials  and  when  two  grounds  are  used,  one 
should  be  connected  through  a  condenser  to  the  instru- 
ments. The  author  has  even  made  use  of  a  small  aerial 
suspended  in  an  attic,  a  brass  bed  in  an  upper  story  of  a 
residence;  and  for  very  short  distances  such  common 
things  as  dishpans,  bed  springs,  and  what  not!  may  be 
utilized  if  nothing  else  is  obtainable.  During  some  ex- 
periments in  Tripoli,  Mr.  Marconi  is  reported  to  have  laid 
both  the  aerial  and  a  similar  set  of  conductors  to  act  as  a 
ground  directly  on  the  sand,  parallel  to  the  direction  in 
which  the  signals  were  to  be  sent.  It  is  said  that  no  aerial 
supports  were  necessary  because  the  sand  was  perfectly 
dry  and  resembled  glass  in  its  conducting  properties. 
These  items  are  merely  suggested  as  suitable  makeshifts 
in  case  other  and  more  business  like  arrangements  are  not 
practicable  and  good  results  may  be  obtained  with  them 
by  exercising  reasonable  skill. 

The  supports  should  take  the  form  of  natural  supports 
whenever  possible  as  this  will  save  considerable  expense. 
Thus  short  extensions  to  trees,  houses  and  building  tops, 
and  similar  structures  make  excellent  supports.  Permis- 
sion may  often  be  obtained  from  the  local  telephone  or 
light  companies  to  place  extensions  on  one  or  more  of 
their  poles  so  that  they  will  not  interfere  with  the  regular 
service  and  some  companies  will  even  give  aid  if  properly 
approached.  The  author  has  utilized  such  poles  for  his 
experiments  for  a  good  many  years. 


22  Experimental  Wireless  Stations. 

The  erection  of  large  poles  from  the  ground  up  is  a 
difficult  task  and  one  which  had  best  be  referred  to  the 
company  which  sells  the  pole  or  else  to  experienced  erec- 
tors. 

Good  straight  grained  2x2  stock  is  suitable  for  small 
poles  up  to  40  feet,  and  the  size  mentioned  is  preferably 
arranged  into  two  or  three  lengths.  Perhaps  the  best  sup- 
port for  experimental  stations,  when  natural  supports 
are  not  available,  is  iron  pipe.  This  form  of  support  may 
also  be  used  in  addition  to  natural  supports  such  as  house- 
tops, etc.  The  height  of  the  aerial  should  always  be  suf- 
ficient to  clear  objects  between  stations  if  possible.  For 
experimental  purposes  a  height  of  about  50  feet  is  a  good 
average,  though  a  higher  one  is  preferable  when  possible. 

After  the  height  has  been  determined,  the  other  di- 
mension to  be  considered  is  the  spread  of  the  aerial.  In 
many  cases  a  low  height  can  be  compensated  by  a  corre- 
sponding increase  in  the  aerial  spread.  However,  since 
an  increase  in  the  horizontal  spread  of  an  aerial  also  in- 
creases the  minimum  wave  length  of  the  transmitted  im- 
pulses, this  dimension  must  be  limited  so  that  the  mini- 
mum wave  length  will  be  about  150  meters  if  the  wave 
length  is  to  be  limited  to  200  meters  or  less,  the  difference 
being  left  to  the  adjustment  of  the  transmitting  induct- 
ance. When  possible  it  is  a  good  plan  to  have  a  duplex 
aerial,  which  is  nothing  more  or  less  than  two  separate 
aerials,  one  for  receiving  and  sending  in  short  wave 
lengths,  and  the  other  for  receiving  in  the  commercial 
wave  lengths,  but  not  for  sending.  While  this  means  two 
separate  aerials  and  should  be  regarded  as  such,  much 
ingenuity  may  be  used  in  utilizing  the  same  supports  for 
the  two  aerials.  Thus  one  may  be  supported  some  dis- 
tance below  the  other,  and  similar  arrangements  may  be 
carried  out  in  a  variety  of  ways.  The  main  objection 


Design  for  Aerials. 


23 


to  a  duplex  aerial  is  that  part  of  the  transmitted  energy 
is  absorbed  by  the  idle  aerial.  (See  fig.  4.)  This  can  be 
overcome  to  an  extent  by  placing  the  two  aerials  at  right 
angles  to  each  other. 

The  large  receiving  aerial  of  a  duplex  system  may 
have  a  length  of  from  100  to  1,000  feet  depending  on 
the  individual  conditions, — about  400  feet  being  a  good 
length.  The  length  means  the  effective  length  including 
the  several  parts.  For  the  vertical,  horizontal,  or  dipped 


FIG. 


FIC.-d.B 


A. — Al — receiving  aerial.  1-2  leads.  A2 — sending1  aerial.  B 
— Al — A2 — divided  aerial.  1-2-3  leads.  Transmitting — short 
circuit  2-3  and  use — or  leave  2-3  open  and  use  either  1  or  2. 
Receiving — use  1 — with  2-3  closed,  other  variations  also. 

aerial  (straightaway)  the  length  of  one  of  the  wires  is  the 
effective  length.  (See  the  figures.)  The  effective  length 
of  the  T  aerial  is  the  length  of  the  vertical  part  plus  one- 
half  of  the  horizontal  portion,  while  that  of  the  reversed 
L  aerial  is  the  length  of  the  horizontal  part  plus  the  length 
of  the  vertical  portion.  In  a  loop  aerial  the  length  is  the 
sum  of  the  lengths  of  the  sides  of  the  reversed  U  loop. 
With  the  ordinary  umbrella  aerial,  the  length  is  roughly 
equal  to  the  length  of  one  of  the  uniform  aerial  conduc- 
tors, as  is  also  the  case  in  a  directive  aerial  having  several 
independent  and  uniform  conductors.  In  order  to  keep 


24  Experimental  Wireless  Stations. 

within  the  limits  of  the  standard  short  wave  length,  an 
effective  length  of  120  or  125  feet  should  not  be  exceed- 
ed.* The  transmitting  aerial  should,  therefore,  be  made 
so  that  the  effective  length  is  within  this  limit.  It  is 
understood  that  the  length  of  the  lead-in  is  included  in  the 
effective  length.  The  effective  length  is  really  the  dis- 
tance from  the  transmitting  instruments  to  the  aerial 
proper,  plus  the  effective  length  of  the  aerial  itself.  In 
case  a  long  ground  lead  is  necessary  to  secure  a  ground  to 
the  instruments,  its  length  must  also  be  added  to  the 
effective  length.  In  the  latter  case,  the  aerial  itself  must 
obviously  be  still  further  limited.  It  is  suggested  that  the 
short  length  can  be  partially  compensated  for  by  making 
the  capacity  of  the  aerial  correspondingly  larger,  but  this 
must  not  be  carried  too  far  so  that  the  capacity  is  too 
large  for  the  charging  capacity  of  the  sending  instru- 
ments. It  is  understood  that  the  capacity  of  the  aerial 
can  be  increased  by  adding  more  wires  to  it.  A  large 
electrostatic  capacity  in  the  aerial  means  greater  energy 
and  more  power  in  the  transmitted  waves  provided  the 
transmitting  instruments  are  able  to  charge  it  with  a 
sufficient  potential.  The  wires  should  always  be  arranged 
symmetrically  and  evenly  spaced  in  order  to  decrease  the 
effect  of  mutual  induction  between  the  adjacent  wires  as 
much  as  possible.  An  increase  in  the  conductors  of  the 
aerial  does  not  increase  the  capacity  to  a  corresponding 
extent  on  account  of  this  mutual  induction.  The  distance 
between  the  respective  conductors  of  an  ordinary  aerial 
should  not  be  less  than  .02  of  their  common  length.  Thus 
in  an  aerial  100  feet  long,  the  wires  should  be  spaced 
at  least  2  feet  apart,  or  even  more  if  possible.  In  addition 


*  This  means  that  the  length  of  the  aerial  proper  should 
not  exceed  75  feet,  in  order  to  allow  for  lead-ins. 


Design  for  Aerials.  25 

to  increasing  the  capacity  of  the  aerial,  an  increase  in  the 
number  of  conductors  decreases  the  resistance.  A  mini- 
mum of  three  wires  and  a  maximum  of  8  or  10  is  the 
range  of  the  number  of  conductors  suitable  for  the  aver- 
age experimental  station  and  it  is  not  desirable  to  exceed 
these  limits.  Some  results  may  of  course  be  had  with 
even  a  single  conductor,  but  for  efficiency  a  plurality  of 
conductors  is  desirable. 


FIG,  S, 


The  number  of  conductors  used  affects  the  transmis- 
sion more  than  the  reception  of  signals.  It  is  desirable 
to  use  two  conductors  placed  6  feet  apart  instead  of  four 
wires  only  nine  or  twelve  inches  apart  and  the  same  rule 
may  be  applied  for  other  dimensions,  since  much  of  the 
effect  of  the  extra  wires  is  lost  by  reason  of  their  close 
proximity.  When  only  two  wires  are  used,  they  should 
of  course  have  a  correspondingly  increased  capacity.  In 
any  case,  the  size  of  the  aerial  conductors  should  not 
exceed  No.  8,  since  larger  sizes  are  wasteful  and  of  pro- 
hibitive weight.  No.  12  is  a  convenient  size  for  experi- 


26 


Experimental  Wireless  Stations. 


mental  aerials.     The  constructional  details  will  be  more 
fully  taken  up  a  little  later. 

For  short  wave  lengths,  the  author  considers  that  the 
umbrella  aerial  or  perhaps  a  modified  umbrella  will  prove 
the  most  satisfactory  because  of  the  large  capacity  which 
is  possible  in  a  small  space.  Suitable  forms  for  this  type 


FIC.G. 


of  aerial  are  indicated  in  fig.  5.  This  aerial  is  called  the 
umbrella  presumably  by  reason  of  its  resemblance  to  the 
ribs  of  the  umbrella.  This  arrangement  may  easily  be 
converted  into  a  directive  aerial  as  shown  in  fig.  6,  in 
which  form  it  will  doubtless  be  the  most  useful  to  experi- 
menters. The  several  conductors  are  preferably  insulated 
from  each  other  in  this  case,  though  they  may  be  con- 
nected together  at  the  top  or  pole  end.  Each  wire  is  sep- 


Design  -for  Aerials.  27 

arately  connected  to  a  single  pole  switch,  preferably  of 
the  common  porcelain  base  type.  With  this  arrangement, 
one  or  more  wires  may  be  used  independently  from  the 
remainder,  or  all  may  be  used  if  considerable  capacity  for 
transmitting  purposes  is  desired.  This  form  of  aerial  is 
well  adapted  to  experimental  purposes  and  has  the  addi- 
tional advantage  of  being  mechanically  strong  and  requir- 


FIG.V. 


FIG. a. 


FIG.  9 


ing  only  a  single  pole  support.  This  type  of  aerial  is  par- 
ticularly suited  to  house  tops,  the  roofs  of  buildings,  and 
similar  places. 

In  congested  places  where  the  available  space  for  the 
aerial  is  limited,  as  on  ships,  various  types  of  horizontal 
or  flat  top  aerials  are  used.  Experimenters  will  find  these 
types  well  adapted  to  their  purposes.  These  aerials  are 
also  known  by  names  which  correspond  to  their  respective 
shapes.  The  reversed  L  type  is  shown  in  fig.  7,  and  is 
highly  directive  by  reason  of  its  shape.  The  maximum 
radiation  is  in  a  direction  opposite  to  that  in  which  its 


28  Experimental  Wireless  Stations. 

free  end  points  and  it  also  receives  signals  at  the  best 
from  the  same  general  direction.  The  leads  are  taken  off 
from  one  end  of  the  aerial,  and  if  the  two  ends  are  of 
uneven  length,  the  lead  should  be  taken  off  from  the  lower 
end.  In  the  latter  case,  the  aerial  is  called  an  inclined 
aerial.  When  the  leads  are  taken  off  in  the  form  of  a  T 
as  in  fig.  8,  signals  are  sent  and  received  the  best  in  the 
plane  of  the  aerial,  but  the  directive  effect  is  considerably 
less  than  with  the  L  type.  Instead  of  taking  the  leads  off 
at  right  angles  it  is  often  necessary  or  convenient  to  take 
them  at  an  angle  to  form  an  oblique  lead.  The  several 
wires  are  preferably  connected  together  at  one  end,  al- 
though this  is  not  essential. 

By  taking  a  double  lead  as  illustrated  in  fig.  9,  either 
as  a  T  or  L  type,  a  looped  aerial  is  formed.  This  inverted 
U  type  is  adapted  to  close  tuning  and  eliminates  humming 
caused  by  neighboring  telephone  and  power  lines.  These 
types  may  of  course  be  considerably  varied,  but  a  simple 
form  is  desirable  in  order  to  secure  close,  sharp  tuning. 

Having  gained  some  idea  of  the  several  types  and 
general  features  of  aerials,  some  of  the  constructional 
details  will  now  be  considered. 

INSULATORS. 

It  is  important  that  the  aerial  be  suspended  so  that  it 
is  thoroughly  insulated.  The  insulation  should  be  effect- 
ive during  all  kinds  of  weather  and  faulty  insulation 
should  be  avoided  with  considerable  care  if  an  efficient 
station  is  desired. 

Hard  rubber,  fibre,  and  unglazed  porcelain  are  not 
very  desirable  as  aerial  insulators.  A  material  known  bv 
the  trade  name  of  Electrose  is  made  into  a  number  of 
suitable  forms.  This  type  of  insulator  is  also  mechanic- 


Design  for  Aerials.  29 

ally  strong,  since  metal  rings  are  molded  directly  into 
the  insulating  material.  Corrugations  are  provided  to 
increase  the  distance  over  which  a  surface  charge  must 
pass  and  also  serve  to  prevent  the  formation  of  a  con- 
ducting film. 

Aerials  for  transmitting  purposes  are  necessarily  bet- 
ter insulated  than  those  used  for  receiving  purposes  only, 
but  in  any  case  the  aerial  conductors  should  not  touch 
foreign  or  partially  conductive  materials.  Common  two 
wire  glazed  porcelain  cleats  make  convenient  insulators 
for  small  stations.  These  may  be  had  for  a  few  cents 
a  piece.  The  holes  are  \y2  inches  apart,  so  that  a  single 
cleat  is  sufficient  insulation  for  a  receiving  aerial  and  also 
for  a  transmitting  station  in  which  only  100  watts  or  a 
one  inch  coil  is  used. 

When  more  power  or  larger  coils  are  to  be  used,  sev- 
eral of  these  cleats  may  be  arranged  in  tandem.  The 
cleats  may  be  joined,  and  used  by  passing  wire  through 
the  two  holes  so  that  the  wire  to  be  insulated  is  separated 
by  the  insulator  from  the  wire  attached  to  the  support. 
There  are  various  other  forms  of  porcelain  and  glass 
insulators  which  may  be  had  at  supply  houses  and  since 
they  are  all  used  in  much  the  same  manner,  no  further 
comment  seems  necessary.  Strain  insulators  are  useful 
in  breaking  up  the  guy  wires  used  in  supporting  the  poles, 
so  that  the  transmitted  waves  are  not  unduly  absorbed. 
This  form  of  insulator  is  also  useful  for  the  main  aerial 
supports.  The  leads  or  lead-in  wires  should  be  insulated 
with  the  same  care  as  the  aerial  itself.  The  supports 
which  hold  the  leads  should  have  insulations  of  the  same 
general  nature  as  that  provided  for  the  aerial. 

A  problem  is  sometimes  presented  when  it  comes  to 
bringing  the  wires  into  the  building.  A  good  way  is  to 


30 


Experimental  Wireless  Stations. 


bore  holes  for  the  wires,  in  a  glass  window.  Heavy  por- 
celain tubes  placed  in  holes  in  the  woodwork  are  also 
suitable  for  small  stations.  A  fairly  good  lead-in  insu- 
lator can  be  made  by  using  a  nest  of  tubes,  one  over  the 
other,  starting  with  a  half  inch  in  outside  diameter  and 
ending  in  the  largest  convenient  outside  diameter.  A 


Ft 


a. — W. — window.  H. — hole  in  glass.  3 — insulator  to  take  up 
strain.  L — Lead-in,  b. — P — windowpane.  K — slide  casing.  B 
board  with  insulators,  window  casing  rests  on  B.  c. — Tl.  T2 — 
Porcelain  tubes. 


number  of  special  insulators  may  be  had  at  supply  houses. 
See  fig.  10  for  several  details  of  construction  for  the 
lead-ins.  The  wires  should  be  anchored  by  an  insulator 
just  before  entering  the  building  in  order  to  take  up  the 
strain. 

The  general  manner  of  suspending  an  aerial  is 
illustrated  in  fig.  11.  The  spreaders  can  be  of  wood  or 
bamboo.  Curtain  poles  are  suitable  for  this  purpose. 
Twisted  wires,  screw  eyes,  mast  withes  and  similar  hard- 


Design  for  Aerials. 


31 


ware  or  improvised  hardware  are  useful  in  fastening  the 
insulators  and  supports. 

ASSEMBLING.— CONDUCTORS. 

In  assembling  the  aerial  conductors  and  the  spreaders, 
it  is  advisable  to  arrange  everything  on  the  ground  first. 
The  wires  may  be  of  copper,  tinned  copper,  aluminum, 
or  phosphor  bronze.  Iron  wire  is  not  recommended,  al- 


though it  may  be  used.  The  phosphor  bronze  is  the  most 
desirable  because  it  is  strong,  springy,  and  may  be  had  in 
a  standard  strand  of  seven  No.  22  B&S  conductors.  It 
is  generally  sold  by  the  foot.  Stranded  conductors  have 
a  slight  advantage  over  solid  conductors. 

Although  copper  has  less  than  one-half  the  tensile 
strength  of  phosphor  bronze,  it  is  very  easily  obtained 
and  quite  suited  to  aerials.  It  has  a  good  conductivity, 


32  Experimental  Wireless  Stations. 

is  pliable,  can  be  easily  soldered,  and  may  be  had  in 
strands  if  desired.  Ordinary  No.  12  telephone  copper 
wire  is  suitable  for  experimental  aerials.  The  wire  used 
should  never  exceed  No.  16  or  its  equivalent  in  fineness 
or  No.  8  in  coarseness. 

Aluminum  is  not  so  good  a  conductor  nor  is  it  as 
strong  as  copper  wire,  but  it  is  pliable  and  very  cheap 
when  compared  foot  by  foot.  The  main  difficulties  with 
aluminum  aerials  are  that  the  wires  are  easily  broken  by 
twisting  and  that  a  non-conductive  coating  soon  forms 
which  practically  insulates  the  joints  unless  they  have 
been  well  soldered. 

In  using  aluminum  wires,  kinks,  bends,  and  excessive 
strains  should  be  avoided.  This  also  applies  to  other 
wires.  Aluminum  is  difficult  to  solder  but  special  solders 
are  obtainable  which  make  the  operation  reasonably  sure 
provided  the  joint  is  well  cleaned  to  begin  with.  All 
joints  in  the  aerial  should  be  soldered  and  it  is  also 
advisable  to  tape  them  with  a  good  quality  of  electrician's 
tape  and  rubber  solution.  Loose  contacts  in  an  aerial 
cut  down  the  efficiency  materially  and  also  make  the  aerial 
weak  mechanically.  The  high  frequency  currents  must 
have  as  clear  and  as  good  a  conducting  path  as  possible 
if  the  waves  are  to  be  radiated  without  considerable  loss. 

JOINTS. 

Fig.  12  shows  a  fairly  good  way  to  make  a  joint  with- 
out solder.  The  wires  should  be  cleaned  and  the  joint 
made  tight,  after  which,  wrap  several  layers  of  tinfoil 
about  the  joint  and  tape  well.*  When  the  aerial  is  con- 
structed with  every  concern  for  efficiency,  the  wires  will 

*  These  points  have  appeared  in  several  magazines  and 
in  general  use. 


x 

are  in  general  use. 


Design  for  Aerials. 


33 


be  thoroughly  insulated  even  at  the  points  where  they 
make  contact  with  the  metal  connections  of  insulators. 
This  may  be  done  by  tape,  and  the  chief  object  is  to 
prevent  thermo-electric  and  galvanic  action  between  the 
dissimilar  metals.  Fig.  13  illustrates  a  suitable  joint  for 
lead  wires  which  prevents  the  wire  from  breaking  by  the 
swaying  motion  given  it  by  the  wind.  When  electrician's 
tape  and  liquid  insulation  are  used,  a  very  good  water  and 


-a 


FIG,  IE, 


rust  tight  joint  is  insured.  The  wire  conductors  should 
be  kept  free  from  nicks,  kinks,  and  sharp  bends,  since 
they  are  easily  parted  at  such  points. 

WIRES.— SIZE. 

Large  spans  require  larger  sizes  of  wires  than  short 
spans,  since  they  are  subject  to  greater  strains.  Numbers 
8  to  10  are  suitable  for  spans  in  excess  of  200  feet,  while 
numbers  11  to  15  are  suitable  for  the  shorter  spans.  In 
planning  the  conductors  larger  sizes  should  be  used  when 
aluminum  wire  is  used  than  for  copper,  larger  for  copper 
than  for  phosphor  bronze,  and  larger  sizes  should  also 
be  used  according  to  the  increase  in  the  span. 


34  Experimental  Wireless  Stations. 

AERIAL  SUPPORTS. 

It  is  always  advisable  to  support  the  aerial  by  means 
of  pulleys  and  ropes,  so  that  it  may  be  lowered  for  re- 
pairs when  necessary.  Good  galvanized  pulleys  may  be 
had  at  a  low  price  at  hardware  and  supply  houses  and 
ropes  and  flexible  wires  may  also  be  had  at  these  places. 
Flexible  wire  is  preferable  to  rope,  since  the  latter  re- 
quires frequent  renewals.  The  rope  or  wire  should  al- 
ways be  sufficient  in  size  to  take  up  all  the  strains  as  well 


HE. 


as  a  large  overload.  The  working  strain  of  manila  rope 
may  be  found  by  dividing  the  square  of  the  circumfer- 
ence in  inches  by  8  for  the  strain  in  tons.  Thus,  to  find 
the  size  of  rope  required,  estimate  the  weight,  allowing 
for  excess  strains,  and  multiply  the  resulting  weight  in 
tons  by  8.  Extract  the  square  root  to  get  the  circumfer- 
ence in  inches.  The  safe  strain  for  wire  rope  is  found  by 
multiplying  the  square  of  the  circumference  in  inches  by 
.3  for  iron  and  .8  for  steel  wire.  For  small  aerials  a 
good  grade  of  clothes  line  or  clothes  wire  is  suitable. 


Design  for  Aerials.  35 

LEAD-IN  WIRES. 

The  lead-in  wires  should  have  a  capacity  equal  to  the 
capacity  of  the  aerial.  Thus,  if  the  aerial  is  composed 
of  six  number  12  wires,  the  lead-ins  should  have  a  capa- 
city equal  to  that  of  six  No.  12  wires,  and  this  is  prefer- 
ably obtained  by  twisting  six  No.  12  wires  together.  When 
the  lead-ins  have  a  smaller  capacity  than  the  aerial  itself, 
they  offer  impedence  to  the  high  frequency  oscillations 
and  the  radiation  is  accordingly  reduced.  The  lead-ins 
should  always  be  as  short  and  direct  as  possible  and 
should  be  connected  to  the  lower  end  of  the  aerial.  When 
long  variously  twisted  lead-ins  are  used,  sharp  tuning 
is  practically  impossible.  The  lead-in  wires  are  essentially 
not  intended  to  radiate  the  energy  but  to  conduct  it  up 
to  the  aerial,  from  which  point  it  is  most  efficiently  ra- 
diated. When  this  is  not  possible,  the  aerial  itself  should 
be  extended  directly  to  the  vicinity  of  the  transmitting 
instruments.  The  lead-in  wires  should  have  nearly  a 
straightaway  course,  i.  e.  without  angles,  bends,  joints, 
or  the  like.  If  the  term  may  be  used, — high  frequency 
currents  abhor  all  joints,  kinks,  bends,  and  other  defectt 
in  tht  conductor. 

POLES. 

While  a  number  of  suitable  aerial  supports  have  al- 
ready been  suggested,  a  few  notes  on  poles  may  be  well 
taken.  Many  experimenters  will  find  bamboo  an  excel- 
lent material  for  short  poles  as  well  as  for  aerial  spread- 
ers. Portable  poles  may  be  made  from  this  material. 
Jointed  wooden  poles  are  not  desirable  for  poles  exceed- 
ing 40  feet  in  length,  a  wooden  truss  work  being  more 
suitable  for  larger  poles.  Experimenters  have  made  poles 
from  100  to  150  ft.  high  on  the  truss  plan  without  great 


36 


Experimental  Wireless  Stations. 


difficulties.     In  this   form  of  construction,  the  pole  is 
built  up  in  the  form  of  a  long,  narrow  pyramid  with  a 


FIG.  14 


base  so  that  the  builders  can  construct  it  piece  by  piece. 
(See  fig.  14.) 

Iron  pipe  makes  a  good  material  for  aerial  poles.  The 
pipe  can  be  had  at  any  plumbers'  or  hardware  supply 
house  in  nearly  every  locality.  The  stock  should  be  what 
is  known  as  "heavy."  The  pole  may  be  made  in  sections, 
the  lower  section  being  the  largest  and  the  upper  section 


Design  for  Aerials.  37 

the  smallest  of  the  progression.  The  sections  are  joined 
by  reducing  couplings,  and  the  dealer  should  be  consulted 
for  suitable  sizes  and  dimensions.  It  will  be  convenient 
to  have  the  dealer  cut  and  thread  and  fit  the  pipe  unless 
the  reader  has  experience  and  tools  for  this  purpose.  The 
pole  and  the  joints  should  be  covered  with  a  water  proof 
paint,  such  as  a  solution  of  asphalt.  A  hole  to  support 
a  pulley  should  be  drilled  near  the  top,  through  which 
the  rope  to  support  the  aerial  is  passed.  It  is  desirable 
to  insulate  the  pole  at  its  base  when  such  procedure  is 
possible.  Sockets  for  this  purpose  may  be  made  from 
insulating  material  or  purchased  from  supply  houses. 

The  dimensions  for  a  40  foot  iron  pipe  pole  follow. 


Sections — three. 

1st.     15  foot  length  of  2  inch  pipe. 
2nd.     15  foot  length  of  1J4  mcn  pipe. 
3rd.     10  foot  length  of  $4  inch  pipe. 

Reducers  of  malleable  iron. 

1st,  between  sections  1  and  2 — 2  by  1J4  mcn  reducer. 
2nd,  between  sections  2  and  3 — 1 J4  by  J4  mch  reducer. 
A  top  ornament  or  closure  may  also  be  provided. 

Guy  wires, — four  wires  at  approximately  a  30  degree 
angle  from  the  top  portion  of  each  section.  Size  of  wires, 
— No.  12  or  14  galvanized  iron.  The  second  and  third 
sets  are  preferably  broken  by  means  of  insulators. 


38  Experimental  Wireless  Stations. 

GUY  WIRES. 

The  experimenter  should  take  considerable  care  to 
make  his  aerial  strong  so  that  it  will  not  need  repairs  after 
every  little  wind  blow.  The  iron  pole  will  not  support 
itself  without  the  aid  of  the  guy  wires.  In  the  case  of 
an  umbrella  aerial  the  conductors  take  the  place  of  the 
top  set  of  guy  wires.  Small  aerials  are  easily  erected 
and  the  guy  wires  may  be  tightened  by  hand.  Turnbuckles 
should  be  provided  for  larger  poles,  however,  in  order  to 
take  up  the  slack.  The  insulators  in  the  guy  wires  should 
be  placed  every  ten  or  fifteen  feet  and  may  be  of  the 
type  already  described.  Strain  insulators  are  preferable 
for  this  purpose,  however. 

While  the  matter  of  aerials  has  now  been  considered 
in  some  detail,  the  minor  details  are  left  to  the  individual 
resources  of  the  reader,  since  the  conditions  vary  widely 
in  each  case.  The  matter  in  this  and  other  parts  of  the 
book  is  intended  largely  as  suggestive  rather  than  dicta- 
tive,  and  various  details  may  be  modified,  provided  that 
the  essential  principles  and  dimensions  are  not  violated. 
It  is  suggested  that  the  umbrella,  variable  directive  aerial, 
T  aerial,  and  directive  aerial  will  be  most  suited  in  the 
order  mentioned,  and  that  the  duplex  idea  should  be 
adopted  if  it  is  desirable  to  receive  from  the  commercial 
stations  without  interfering  with  them. 


CHAPTER  III. 
GROUNDS  AND  LIGHTNING  PROTECTION. 


Equally  or  more  important  than  a  good  aerial  is  the 
item  of  a  good  ground.  The  quality  of  the  ground  con- 
nection materially  affects  the  efficiency  of  a  station  and  its 
operating  range.  Variations  in  the  ground  connection 
may  cause  a  difference  of  failure  or  success.  A  good 
ground  connection,  then,  is  essential  to  an  efficient  wire- 
less station.  The  various  means  for  obtaining  grounds 
may  be  itemized  and  considered  as  follows : 

GROUNDS  IN  WATER. 

This  form  consists  of  a  mass  of  metal  suspended  in 
the  ocean,  a  lake,  a  river,  a  well,  or  a  cistern  and  forms 
a  good  connection.  In  fact,  the  grounding  of  ship  stations 
through  the  hull  affords  a  connection  almost  as  good  as 
metal.  When  connection  is  made  to  a  pump  or  cistern 
pipe,  the  iron  should  be  thoroughly  cleaned  and  the  con- 
ductor soldered  to  it. 

IMBEDDED  GROUNDS. 

A  good  connection  can  generally  be  had  by  burying  a 
large  surface  of  sheet  copper  or  zinc  in  damp  earth,  at 
least  12  feet  below  the  surface  and  preferably  more.  A 
ground  conductor  should  be  soldered  to  the  sheets  which 
should  be  well  connected  to  each  other.  The  sheets  may 


40  Experimental  Wireless  Stations. 

be  in  the  form  of  old  copper  boilers  which  may  be  had 
from  the  scrap  heap,  and  it  is  desirable  to  have  a  total 
surface  equal  to  a  single  flat  sheet,  10  feet  x  10  feet.  It 
is  good  practice  to  imbed  the  sheets  in  between  layers  of 
coke  in  order  to  insure  a  uniformly  good  contact  during 
the  different  times  of  the  year. 

IMBEDDED  GROUNDS.    SPECIAL  FORMS. 

There  are  several  ready  made  grounds  to  be  had  in 
the  market,  but  since  these  are  rarely  intended  for  other 
than  use  for  telephone  lines  and  for  lightning  grounds, 
several  of  them  connected  together  must  be  used  for  an 
effective  wireless  ground.  They  consist  essentially  of 
sheet  copper  formed  so  as  to  present  a  large  surface  to 
the  ground  and  in  some  forms,  a  coke  filling  is  used. 
Chemical  grounds  consist  of  the  ordinary  imbedded 
ground  with  layers  of  coke  and  calcium  chloride,  or  cal- 
cium chloride  alone  around  the  metal.  The  calcium  chlor- 
ide is  very  cheap  and  insures  a  state  of  moisture  about 
the  plates  at  all  times.  About  50  pounds  of  coke  and  25 
pounds  of  calcium  chloride  will  suffice  in  conjunction  with 
100  square  feet  of  imbedded  sheet  metal  to  form  a  very 
good  ground. 

CONNECTION  TO  GAS  AND  WATER  PIPES. 

In  the  cities,  the  gas  and  the  water  supply  pipes  are 
commonly  used,  preferably  the  latter.  Special  ground 
clamps  may  be  had  from  supply  houses  for  a  very  small 
sum  which  are  adapted  for  making  good  connection  with 
the  pipes.  When  the  pipes  are  used  for  a  ground  it  is 
advisable  to  short  circuit  the  meter  by  means  of  a  heavy 
piece  of  wire.  The  wire  from  the  instruments  to  the 
ground  should  be  run  as  straight  and  direct  as  possible 


Grounds  and  Lightning  Protection.  41 

and  all  joints  should  be  soldered.  When  several  pipes, 
as  water,  drain,  and  gas,  are  in  close  proximity  to  each 
other,  it  is  advisable  to  connect  all  of  them. 

For  small  stations  and  also  as  a  separate  lightning 
ground,  an  iron  pipe  or  several  iron  pipes  two  or  three 
inches  in  diameter  and  ten  feet  long  may  be  buried  into 
the  ground  just  outside  of  the  building  in  a  convenient 
position.  The  lower  end  is  preferably  pointed  by  ham- 
mering the  pipes  into  a  V  shape.  (A  blacksmith  can  do 
this  for  you.)  The  ground  wire  should  be  thoroughly 
soldered  with  care  to  this  pipe  and  the  joint  covered  with 
pitch  or  asphaltum.  If  possible  this  ground  should  be 
located  over  a  drain  pipe  or  otherwise  provided  with  a 
supply  of  water. 

INDIRECT  GROUNDS. 

There  are  two  general  types  of  indirect  grounds  and 
neither  is  as  desirable  as  a  good  direct  ground.  In  one 
form,  a  second  aerial  is  constructed  and  suspended  in  a 
position  close  to  but  insulated  from  the  ground.  It  thus 
forms  a  capacity  or  condenser  with  the  ground.  This 
type  is  adapted  to  close  tuning  and  is  convenient  when  a 
direct  ground  is  impracticable  for  one  reason  or  another, 
but  is  considerably  less  efficient.  The  other  form  of 
indirect  ground  is  similar,  except  that  a  large  meshwork 
of  bare  wires  or  a  netting  is  spread  over  the  surface  in 
the  immediate  vicinity  of  the  station  without  insulation, 
so  that  it  makes  both  direct  and  indirect  contact  with  the 
earth.  A  very  large  area  must  be  covered  before  this 
method  is  efficient,  but  it  is  sometimes  used  for  portable 
outfits,  in  which  case  the  network  is  spread  out  in  grass  or 
a  similar  moist  surface  in  preference  to  other  places. 
For  experimental  receiving  purposes  a  fair  ground  may 
be  had  by  driving  a  spike  into  a  tree  and  making  contact 


42  Experimental  Wireless  Stations. 

therewith.  The  steel  frame  of  buildings  may  be  used  as  a 
ground  if  nothing  better  is  obtainable.  In  any  case  the 
ground  wire  should  be  run  direct  from  the  instruments 
and  as  short  as  is  possible. 

THE  GROUND  WIRE. 

It  is  not  necessary  to  insulate  the  ground  wire,  al- 
though it  is  advisable  to  do  so.  When  it  is  over  20  feet 
in  length  it  should  be  well  insulated  to  prevent  loss  from 
induced  currents.  The  use  of  a  ground  wire  no  less  than 
No.  4,  B.  &  S.  in  diameter  is  advised  and  even  larger 
sizes  are  desirable.  Of  course  smaller  sizes  will  serve 
to  a  sufficient  extent  for  experimental  purposes,  but  the 
larger  size  means  a  better  direct  ground.  Grounding 
should  not  be  done  by  connecting  to  gas  or  electric  fix- 
tures, since  these  are  often  insulated  from  the  ground  and 
in  any  case  afford  poor  connections. 

PROTECTION  FROM  LIGHTNING. 

Wireless  aerials  do  not  attract  lightning,  as  the  term 
is  generally  understood,  but  they  do  accumulate  undesir- 
able static  charges  during  the  stormy  part  of  the  year. 
When  well  grounded  OUTSIDE  of  the  building,  the 
aerial  forms  an  EFFICIENT  LIGHTNING  ROD  and 
actually  protects  the  station  and  surrounding  buildings. 
These  facts  have  been  ascertained  by  the  author  by  num- 
erous experiments  and  although  the  author's  station  has 
been  struck  several  times,  no  damage  has  ever  resulted. 
Experiments  were  carried  out  with  a  condenser  and  gap 
in  the  aerial  during  the  electrical  storms  and  large  charges 
were  accumulated  and  experimented  with  at  such  times. 
Inasmuch  as  the  experiment  is  attended  with  some  danger, 
its  repetition  is  not  recommended.  In  the  experiences  of 


Grounds  and  Lightning  Protection. 


43 


others  with  which  the  author  is  acquainted,  several  cases 
have  presented  warnings.  In  one  case,  the  operator  had 
his  ears  pierced  while  receiving  (or  trying  to),  from 
which  it  may  be  inferred  that  it  is  NOT  ADVISABLE  to 
operate  during  severe  local  storms.  In  another  case,  the 
operator  had  his  aerial,  which  was  a  high  one,  well 
grounded  and  no  harm  resulted  to  it  or  the  immediate 
neighborhood,  while  a  grocery  a  block  away  was  com- 
pletely demolished.  It  is  always  desirable  to  ground  your 


FiG.ia. 


re. 


aerial  during  storms  and  at  all  times  when  it  is  not  in 
use.  This  is  conveniently  accomplished  by  means  of  a 
double  throw  switch  on  the  outside  of  the  building  so 
that  the  aerial  is  grounded  to  an  outside  ground  when 
not  in  use.  The  ground  connection  should  be  No.  4  B. 
&  S.  wire  or  even  larger  and  very  direct.  (See  fig.  15.) 
The  switch  should  have  a  carrying  capacity  of  25  or  30 


44 


Experimental  Wireless  Stations. 


amperes.     Fifty  or  100  ampere  switches  are  the  standard 
size. 

AN  EFFICIENT  LIGHTNING  PROTECTION. 

This  arrangement  takes  advantage  of  the  fact  that 
the  high  frequency  surges  abhor  impedence  from  a  choke 
coil.  The  choke  coils  are  in  fact  more  advantageous  than 
insulators  would  be.  See  fig.  16  for  the  connections.  The 


FIG.  IE 


s.e  Sw'.t 


,,,-»., 

«)/ 

& 


CK,K«  Coils 


D.P.  SWltvJl 


^mmj-^i^ 


S.  P.  S wi 


When    using    instruments    open    (4),    close    (1),    (2)    and    (3). 
When  not  using  instruments  open  (3),  (1),  and  (2).     Close  (4). 


main  switch  should  be  able  to  carry  30  amperes  and  when 
the  station  is  in  use  the  choke  coils  are  short  circuited  by 
the  auxiliary  switches  so  that  they  will  not  impede  the 


Grounds  and  Lightning  Protection.  45 

transmitted  impulses.  This  arrangement  prevents  the 
charge  from  damaging  the  instruments  or  the  building. 
The  choke  coils  are  made  by  winding  30  turns  of  No.  4 
B.  &  S.  wire  on  a  large  porcelain  tube,  two  or  three  inches 
in  diameter. 

Lightning  grounds  should  always  be  carried  out  to 
the  outside  of  the  building  or  station  and  if  the  regular 
ground  does  not  meet  this  requirement,  a  separate  ground 
must  be  used.  Ordinary  short  gap  lightning  arresters 
are  useless  in  wireless  stations,  because  the  transmitted 
impulses  jump  the  short  gap  the  same  as  lightning  does. 

The  lightning  protection  for  a  station  does  not  cost 
a  great  deal  and  is  well  worth  while.  It  is  one  of  the 
first  items  which  should  receive  attention,  particularly  in 
mountainous  regions. 

When  the  station  is  not  to  be  used  for  a  long  time, 
as  during  a  vacation  trip,  it  is  desirable  to  lower  the  aerial 
conductors  so  that  the  liability  to  become  blown  down 
by  winds  or  be  struck  by  lightning  is  entirely  removed. 

It  is  not  necessary  to  take  the  aerial  down  during  stor- 
my weather,  however,  or  even  desirable,  provided  that  it 
is  well  grounded. 


CHAPTER  IV. 


GENERAL  FEATURES  OF  THE  TRANSMITTER. 
RESONANCE. 

In  arranging  the  material  for  this  book,  the  author 
spent  considerable  time  in  selecting  a  logical  order  for  the 
several  items  and  it  is  suggested  that  the  most  benefit  will 
result  from  a  consideration  of  the  matter  in  the  order 
given.  It  is  certainly  possible  and  perhaps  even  desirable 
to  start  in  with  any  one  chapter  and  to  find  the  desired 
matter  without  reading  through  matter  of  indirect  interest. 
In  the  present  chapter  the  general  features  of  the  trans- 
mitter together  with  a  consideration  of  resonance  is  to 
be  considered,  and  it  is  suggested  that  this  matter  be  un^ 
derstood  before  referring  to  the  chapters  on  the  several 
details. 

To  begin  with,  we  are  only  to  consider  tuned  transmit- 
ters, i.  e.  those  which  are  coupled  to  the  antenna  circuit. 
There  are  two  general  types  of  coupled  transmitters,  the 
direct  coupled  and  the  indirect  or  inductively  coupled. 
Each  has  certain  characteristics  which  will  be  considered 
more  fully.  The  exact  circuits  employed  are  of  course 
somewhat  varied,  but  since  the  general  features  are  the 
same  the  circuit  shown  in  fig.  17  may  be  regarded  as  typ- 
ical of  the  direct  coupled  type,  while  that  shown  in  fig. 
18  may  be  regarded  as  typical  for  the  inductively  coupled 
type.  For  the  present  the  circuits  will  be  regarded  as 
excited  only  by  means  of  ordinary  spark  gaps.  Other 


The  Transmitter. — Resonance. 


47 


means  for  excitation  which  are  within  the  limits  of  the 
average  experimenter,  will  be  considered  in  detail,  later. 

The  first  point  to  be  thoroughly  understood  is  that  the 
transmitting  circuits  are  oscillatory  in  nature  and  that  the 
transmitted  impulses  are  radiated  as  waves  having  char- 
acteristic properties.  In  wireless  transmitters,  the  essen- 
tial characteristics  of  the  circuits  are  that  they  may  be 
caused  to  vibrate  at  a  very  high  rate.  The  phenomena 
is  very  much  like  other  vibrations.  For  instance,  in  sound, 
if  a  bell  is  struck  a  sharp  blow,  it  vibrates  and  the  vibra- 


FIG.  17 


tions  in  turn  cause  sound  waves  to  be  radiated  from  the 
surface  of  the  bell.  The  loudness  of  the  sound  will  vary 
according  to  the  dimensions  of  the  bell  and  the  force  with 
which  it  is  struck.  The  tone  of  the  resulting  sound  will 
also  vary  according  to  the  dimensions  of  the  bell  itself, 
i.  e.  its  characteristic  dimensions  and  vibratory  period. 

In  a  wireless  transmitter,  we  have  the  same  features. 
The  current  which  causes  a  high  potential  to  charge  a 
condenser,  corresponds  to  the  force  which  strikes  a  bell. 


48 


Experimental  Wireless  Stations. 


The  condenser  in  turn  sets  up  vibrations  in  the  circuits 
so  that  waves  are  radiated  from  the  antenna,  in  much  the 
same  manner  as  the  vibrations  of  the  bell  cause  sound 
waves  to  be  radiated.  In  fact  the  difference  in  the  waves 
radiated  by  the  bell  and  a  wireless  transmitter  lies  in  the 
characteristic  properties  (wave  length,  frequency,  per- 
sistency, etc.)  and  in  the  medium  through  which  the  re- 
spective radiations  are  carried.  (Air  for  sound  and  ether 
(space)  for  wireless  waves.) 

Now  then,  the  circuits  of  the  transmitter  can  be  vi- 
brated the  same  as  a  bell  is  vibrated  and  the  character 


FIE.  1 6. 


of  the  radiations  will  vary  according  to  the  electrical  di- 
mensions of  the  circuits  and  the  force  with  which  they 
are  set  into  vibration.  This  is  the  keynote  to  an  under- 
standing of  the  why  of  wireless  transmission.  We  can 
vary  the  characteristics  of  the  transmitted  radiations  by 
changing  the  electrical  dimensions  or  vibratory  period  of 
the  transmitting  circuits.  This  is  accomplished  by  adding 
or  subtracting  capacity  or  inductance  or  both,  in  much  the 
same  manner  as  a  violinist  varies  the  effective  length  of 
a  given  string  to  produce  different  tones.  It  is  understood 
that  even  the  slightest  change  in  the  capacity  or  induct- 


The  Transmitter. — Resonance.  49 

ance  of  a  circuit  changes  its  electrical  dimensions  and 
also  changes  the  period  or  rate  of  vibration.  The  actual 
vibration  in  the  circuits  is  caused  by  the  surgings  of  the 
discharge  from  the  condenser,  or  as  it  is  more  often 
termed,  the  oscillatory  discharge  of  the  condenser. 

By  the  referring  to  fig.  17,  in  which  A  represents  the 
aerial,  G,  the  ground,  I,  the  inductance  which  may  be 
varied  and  which  also  couples  the  condenser  and  the  an- 
tenna circuits,  C,  the  condenser,  S,  the  spark  gap,  T,  a 
transformer  or  spark  coil,  B,  a  source  of  current  and 
K,  a  circuit  closing  key,  it  will  be  obvious  that  when  the 
key  K  is  closed  the  transformer  or  coil  T,  which  is  wound 
to  produce  a  high  potential  at  the  secondary  terminals, 
will  cause  a  spark  at  the  gap  S.  In  practice  the  gap  and 
the  condenser  are  adjusted  so  that  the  condenser  is  first 
charged  and  then  discharged  through  the  gap  S.  Now 
it  has  been  definitely  proven  that  although  the  coil  T  only 
produces  a  secondary  current  at  its  terminals  with  a  fre- 
quency of  say  120  cycles  per  second,  this  same  current 
when  used  to  charge  the  condenser  C  and  subsequently 
discharged  through  the  gap  S,  causes  an  oscillatory  cur- 
rent to  discharge  in  the  gap  S  which  may  have  a  frequency 
enormously  greater  than  the  original  frequency  of  120 
cycles  per  second.  This  high  vibration  may  in  fact  be 
as  much  as  250,000  per  second  or  even  more.  It  is  this 
high  rate  of  oscillation  in  the  condenser  circuit  which 
causes  radiations  to  be  sent  out,  as  has  already  been  ex- 
plained. The  condenser  circuit  through  the  gap  S,  and 
the  inductance  I,  (the  oscillations  do  not  pass  through  the 
secondary  of  T  on  account  of  the  high  resistance  offered), 
is  the  actual  part  of  the  wireless  transmitter  which  corre- 
sponds to  the  hammer  of  a  bell.  It  differs  from  a  simple 
comparison,  however.  It  is  found  that  the  exact  nature 
of  the  resulting  vibrations  depends  on  the  dimensions  of 


50  Experimental  Wireless  Stations. 

the  several  parts,  S,  C,  and  I.  It  will  be  obvious  that 
the  condenser  in  discharging  through  the  circuit  I,  S,  C, 
at  a  very  high  rate  causes  the  turns  of  I  through  which 
it  passes  to  vibrate  at  a  corresponding  rate.  The  oscilla- 
tions are  thus  made  useful  for  transmission  purposes  by 
forcing  them  to  pass  through  a  part  of  the  inductance  I. 
Now  it  is  further  found,  that  if  the  dimensions  of  circuit 
C,  I,  S,  are  changed,  as  by  adding  or  subtracting  capacity 
or  inductance,  that  the  characteristic  properties  of  the 
resulting  oscillations  are  varied,  in  much  the  same  man- 
ner as  the  tone  from  a  bell  is  varied  if  a  lead  weight  is 
attached  to  its  edge,  or  a  violin  string,  if  its  effective  di- 
mensions are  varied  by  the  fingers  of  the  violinist. 

In  further  considering  the  circuit  C,  I,  S,  it  should 
be  understood  that  for  the  maximum  effect,  the  several 
parts  C,  I,  S,  must  be  adjusted  or  varied  so  that  they  mu- 
tually contribute  to  produce  the  maximum  effect.  It  is 
obvious  that  if  there  is  too  much  capacity,  the  circuit  will 
be  unbalanced  and  consequently  the  coil  T  will  not  be 
able  to  fully  charge  it.  Or  if  the  gap  S  is  too  long  the 
condenser  will  not  discharge  through  it,  while  if  too  short, 
the  condenser  will  not  be  fully  charged  before  it  dis- 
charges. Or  further,  if  the  number  of  turns  of  I  in  the 
circuit  is  too  many  or  too  little,  the  circuit  will  also  be 
unbalanced.  In  any  case  or  combinations  of  any  single 
cases,  the  result  will  be  similar  to  that  when  an  excessive 
weight  is  attached  to  the  rim  of  a  bell,  that  is,  the  circuit 
through  C,  I,  and  S,  cannot  vibrate  properly.  If  the  dif- 
ference between  the  adjustment  and  the  ideal  adjustment 
is  not  great,  the  oscillatory  effect  will  not  be  stopped,  but 
the  properties  of  the  oscillations  will  be  correspondingly 
varied.  In  practice  it  is  generally  found  that  there  is  a 
certain  adjustment  for  the  circuit  which  produces  a  max- 
imum result.  It  is  of  course  understood  that  any  change 


Transmitters. — Resonance.  51 

in  the  dimensions  of  the  parts  of  the  circuits  causes  a 
change  in  the  natural  wave  length  of  the  circuit  and  the 
resulting  oscillations,  the  same  as  changing  the  diameter 
of  a  bell  produces  a  different  tone.  Changing  either  the 
inductance  or  capacity  in  even  small  amounts  causes  a 
noticeable  change  in  the  wave  length  and  intensity  of  the 
resulting  oscillations.  The  parts  of  the  circuit  have  been 
arranged  in  definite  mathematical  formulas  so  that  the 
proper  dimension  for  the  several  parts  to  produce  a  given 
result  with  a  given  station  can  be  worked  out  by  a  simple 
mathematical  operation.  This  feature  will  be  considered 
a  little  later. 

Now  then,  by  referring  to  this  same  figure  (17),  it 
will  be  obvious  that  when  an  oscillatory  current  passes 
through  some  of  the  turns  of  I,  that  oscillations  will  also 
be  set  up  in  the  antenna  circuit  A,  I,  G,  by  mutual  induc- 
tion between  the  portions  of  the  turns  of  I  included  re- 
spectively in  the  antenna  and  in  the  condenser  circuit. 
The  ratio  and  relation  of  the  respective  turns  included  in 
the  antenna  and  the  condenser  circuits  determine  the  de- 
gree of  coupling  between  the  two  circuits.  The  oscilla- 
tions in  the  inductance  I  are  of  very  high  frequency,  as 
has  already  been  explained,  and  the  two  portions  of  the 
inductance  act  as  a  transformer.  The  inductance  I  forms 
in  fact  an  auto  transformer  (step  up).  Now  then,  the 
voltage  as  well  as  the  frequency  through  the  part  of  I 
included  in  the  condenser  circuit  is  very  high  so  that  the 
frequency  through  the  antenna  circuit  is  of  substantially 
the  same  frequency  but  a  much  higher  potential,  on  ac- 
count of  the  ratio  between  the  turns  included  in  the  two 
respective  circuits.  The  antenna  circuit  is  thus  supplied 
with  a  very  high  potential  high  oscillatory  charge,  cor- 
responding to  the  oscillatory  discharge  of  the  condenser 
C.  The  antenna  circuit  is  consequently  very  powerfully 


52  Experimental  Wireless  Stations. 

vibrated  and  as  a  result  radiations  are  transmitted  from 
this  circuit  in  much  the  same  manner  as  sound  waves  are 
transmitted  from  the  surface  of  a  bell,  except  the  sound 
waves  are  transmitted  through  air,  while  electromagnetic 
waves  are  transmitted  through  the  ether  and  are  caused 
by  the  intimate  relation  of  the  vibrating  antenna  circuit 
with  the  ether,  which  presumably  disturbs  the  ether  at  a 
corresponding  rate.  It  is  understood  that  the  term 
"ether"  is  the  name  for  an  all  prevailing  material  which 
is  imagined  and  assumed  to  exist  and  to  carry  this  elec- 
trically generated  vibratory  motion  in  the  same  general 
way  in  which  the  air  carries  the  sound  waves. 

Now  the  exact  nature  of  the  radiations  is  determined 
by  the  dimensions  of  the  antenna  and  condenser  circuits, 
while  their  power  is  determined  by  the  primary  generating 
source  as  well. 

RESONANCE. 

Resonance  in  the  transmitter  means  the  method  or  art 
of  producing  resonant,  attuned,  or  syntonic  relations  in 
and  between  the  condenser  and  antenna  circuits  and  is 
also  further  carried  out  between  the  condenser  and  the 
transformer  or  coil  T,  when  maximum  results  are  desired. 
In  fig.  17,  the  condenser  C,  and  transformer  T  are  in 
resonance  when  the  capacity  of  C  is  adjusted  so  that  it 
is  just  enough  and  not  too  much  to  efficiently  and  econom- 
ically receive  a  charge  and  discharge  the  same.  This  re- 
lation can  be  determined  by  a  simple  mathematical  opera- 
tion from  a  formula,  which  will  be  fully  presented,  later. 
Now,  then,  with  the  condenser  determined,  its  capacity 
must  necessarily  remain  the  same  for  a  given  coil  T,  so 
that  if  the  circuit  through  C,  I,  and  S,  is  to  be  brought 
into  resonance,  the  respective  parts  must  be  suited  to  the 
given  capacity.  The  gap,  S,  is  of  itself  a  minor  item,  the 


Transmitters. — Resonance.  53 

essential  features  being  an  ability  to  handle  the  full  dis- 
charge currents  without  undue  heating  and  to  be  of  the 
proper  length  so  that  the  condenser  is  properly  charged 
and  discharged.  The  main  tuning,  then,  must  be  done  by 
increasing  or  decreasing  the  number  of  turns  of  the  in- 
ductance I,  through  which  the  condenser  circuit  must  dis- 
charge. Now  a  wire  or  ribbon  conductor,  such  as  is 
used  for  constructing  the  inductance  I,  has  both  capacity 
and  inductance,  though  the  latter  is  in  great  excess  so 
that  the  capacity  is  nearly  negligible.  .  In  a  like  manner, 
the  condenser  of  itself  consists  essentially  of  capacity. 
Even  the  connecting  wires  between  the  condenser  and 
the  inductance  have  capacity  and  inductance,  also  resist- 
ance, so  that  in  order  not  to  materially  effect  the  resulting 
oscillations  they  must  be  made  very  short  and  of  large 
capacity  so  as  not  to  impede  the  high  frequency  oscilla- 
tions. 

Every  conductor  has  a  definite  period  of  vibration  for 
electromagnetic  waves,  just  as  every  wire  in  a  piano  has 
a  definite  vibratory  period.  Now  the  separate  periods 
can  be  combined  or  superposed  when  a  number  of  con- 
ductors or  circuits  are  coupled  or  connected  in  much  the 
same  manner  that  two  or  more  notes  from  a  piano  can 
be  caused  to  produce  a  pleasing  or  displeasing  tone.  The 
condenser  circuit,  then,  is  made  up  of  several  parts  which 
must  have  very  little  resistance  and  practically  no  stray 
inductance  or  capacity.  Now,  increasing  the  number  of 
turns  through  which  the  condenser  circuit  passes  also  in- 
creases the  time  of  the  vibrations,  causing  a  correspond- 
ing increase  in  the  wave  length.  The  wave  length  of  the 
oscillations  in  the  condenser  can  thus  be  varied  by  adding 
or  subtracting  the  desired  amount  of  inductance  through 
which  they  pass,  and  the  less  the  number  of  turns  of  in- 


54 


Experimental  Wireless  Stations. 


ductance  included  in  the  circuit,  the  less  will  be  the  wave 
length. 

Now  then,  consider  the  resonant  relations  in  the  an- 
tenna circuit.  It  is  understood  that  the  antenna  itself, 
being  made  up  of  a  plurality  of  spaced  wires,  consists 
essentially  of  capacity  and  also  quite  a  little  inductance. 
The  antenna  forms  the  capacity  of  the  circuit  in  conjunc- 
tion with  the  ground.  The  inductance  of  the  circuit,  then, 
will  be  the  variable  factor  since  the  antenna  is  generally 


FIG.I3. 


P.E. 


a  fixed  item.  The  wave  length  of  the  circuit  A,  I,  and  G, 
then  will  be  varied  according  to  the  variations  in  the 
amount  of  inductance  or  turns  of  I,  included  in  the  cir- 
cuit, in  the  same  manner  as  has  already  been  explained 
for  the  condenser  circuit. 

That  is,  when  the  number  of  turns  of  I,  through  which 
the  antenna  circuit  is  included,  is  increased,  the  wave 
length  of  the  circuit  will  be  increased.  It  will  be  obvious 
that  since  A  is  a  fixed  quantity  the  natural  wave  length 
of  the  antenna  circuit  cannot  be  less  than  that  of  A  and 


Transmitters. — Resonance.  55 

G  without  inductance,*  in  the  circuit  shown  in  fig.  17, 
and  that  the  variations  must  then  be  limited  to  increase 
the  wave  length  of  the  antenna  system.  As  in  the  case  of 
the  condenser  C,  when  the  maximum  results  are  desired, 
the  capacity  of  the  antenna  A  must  be  made  the  proper 
amount  to  begin  with.  This  can  be  accomplished  by  using 
the  length  and  number  of  wires  which  will  produce  a 
capacity  and  inductance  within  the  limits  of  the  minimum 
wave  length  desired.  It  is  possible  to  lower  the  wave 
length  by  means  of  circuit  like  that  of  fig.  19,  in  which 
a  condenser  is  connected  in  series  with  the  ground  circuit, 
but  this  method  is  not  very  desirable.  In  view  of  the  lim- 
ited wave  lengths,  to  which  experimenters  are  morally 
and  legally  assigned,  this  method  can  be  utilized  in  cases 
in  which  aerials  already  in  use  slightly  exceed  the  maxi- 
mum wave  length.  The  disadvantage  of  this  arrangement 
is  that  the  transmission  is  less  efficient. 

But  to  return  to  fig.  17:  In  order  that  the  antenna 
and  condenser  circuits  should  be  in  resonance  with  each 
other,  it  is  necessary  that  the  adjustments  of  the  induct- 
ance I,  be  made  so  that  the  wave  length  of  the  condenser 
circuit  is  the  same  as  the  wave  length  of  the  antenna  cir- 
cuit. The  circuits  will  then  be  in  a  position  to  produce  a 
maximum  radiation.  This  condition  is,  however,  diffi- 
cult to  obtain  exactly  and  is  further  complicated  by  the 
phenomena  of  beats,  that  is,  the  oscillations  in  the  two 
circuits  superpose  and  interfere  with  each  other  so  that 
two  wave  lengths  are  produced  instead  of  one.  This  fea- 
ture will  be  presently  more  fully  discussed.  Now  if  the 
circuits  have  been  brought  into  resonance  so  that  they  are 
both  attuned  to,  say,  300  meters  wave  length,  and  if  it  is 
desired  to  increase  the  transmitting  wave  length,  both  cir- 


*  See  fig.  19  for  exception. 


56 


Experimental  Wireless  Stations. 


cuits  must  be  increased  accordingly.  The  wave  length  of 
the  condenser  circuit  is  increased  by  adding  more  turns 
of  inductance  and  the  maximum  wave  length  for  the  con- 
denser circuit  will  be  reached  when  this  circuit  includes  all 
of  the  inductance.  Since  the  wave  length  depends  on  the 
product  of  the  inductance  and  capacity  of  a  circuit,  the 
maximum  wave  length  of  the  antenna  circuit  will  general- 
ly be  reached  before  the  maximum  wave  length  of  the 
condenser  circuit  is  reached,  so  that  after  all  of  the  turns 
of  the  inductance  of  the  coil,  I,  have  been  included  in  the 
antenna  circuit,  the  wave  length  cannot  be  further  in- 
creased. Increasing  the  inductance  of  the  condenser  cir- 


FIG.  ED. 


r.E 


cuit  in  this  case  will  throw  the  circuit  out  of  resonance. 
The  wave  length  is  thus  limited  by  the  dimensions  of  the 
antenna  A  and  the  inductance  I.  Since  it  is  impractical 
to  have  the  inductance  I  too  large  and  since  the  antenna  A 
is  in  practice  a  fixed  quantity,  the  arrangement  of  fig.  20 
must  be  used  if  extra  long  wave  lengths  are  desired.  This 
method  acts  to  increase  the  natural  wave  length  of  the  an- 
tenna circuit.  The  shunt  antenna  condenser  may  be 
omitted  if  desired.  The  extra  inductance  is  known  as  a 


Transmitters. — Resonance.  57 

loading  coil  and  extremely  long  wave  lengths  may  be  ob- 
tained in  this  manner.  As  in  the  case  of  fig.  19,  however, 
the  efficiency  of  transmission  is  considerably  lowered, 
since  there  is  generally  a  limited  range  of  wave  lengths  at 
which  a  given  station  can  economically  operate.  How- 
ever, for  experimental  purposes,  this  arrangement  can  be 
used  to  attain  very  long  wave  lengths  (those  exceeding 
1,500  or  2,000  meters  in  length),  a  field  as  yet  open  to  the 
experimenter  and  not  morally  restricted  or  forbidden  to 
him.* 

There  is  one  other  case  of  resonance  with  which  the 
experimenter  is  concerned.  When  spark  coils  or  adjust- 
able types  of  transformers  are  used  in  connection  with 
adjustable  condensers  in  the  condenser  circuit,  there  may 
be  more  than  one  adjustment  of  the  condenser,  C,  which 
will  produce  a  maximum  resonance  effect  with  the  in- 
ductance of  both  the  antenna  and  the  condenser  circuit  in 
a  fixed  ratio.  This  is  a  peculiar  harmonic  effect  and  it  is 
remarkable  that  a  maximum  effect  can  be  had  with  two 
different  adjustments  of  the  capacity  through  essentially 
the  same  circuit.  Now  when  the  power  used  in  the  coil 
or  transformer  T  is  decreased,  (as  when  transmitting 
over  a  very  short  distance),  the  condenser  C,  and  the 
other  adjustments  should  also  be  changed  if  the  maximum 
effect  is  to  be  carried  out.  To  sum  up ; — 

The  resonance  relations  and  wave  length  of  a  trans- 
mitter depend  on  the  relations  of  the  circuits  and  the  ad- 
justments of  the  several  parts.  Since  some  of  these  parts 
are  of  fixed  dimensions,  the  others  must  be  adjusted  to 
correspond  with  them  and  co-operate  to  produce  resonant 
circuits.  The  order  of  tuning  is  practically, — 


*  See  chapter  19  for  effect  of  the  new  law. 


58  Experimental  Wireless  Stations. 

1.  The  transformer  or  coil  being  fixed,  the  condenser 
must  be  varied  to  resonate  with  it.     If  the  power  is 
changed,  a  corresponding  change  must  be  made  in  the 
condenser  if  the  maximum  effect  is  to  be  preserved. 

2.  With  the  condenser  a  fixed  quantity,  to  produce  a 
given  wave  length  in  the  condenser  circuit,  the  inductance 
must  be  varied  to  co-operate  with  the  capacity,  and  al- 
though the  wave  length  may  be  greatly  increased,  the  ad- 
dition of  excessive  inductance  cuts  down  the  transmitting 
efficiency. 

3.  The  aerial  being  a  fixed  quantity,  the  antenna  cir- 
cuit can  be  adjusted  for  a  desired  wave  length  by  the  ad- 
dition of  inductance,  but  if  too  much  inductance  is  used, 
with  or  without  a  shunt  capacity,  the  efficiency  of  trans- 
mission is  reduced.    A  series  capacity  may  be  used  to 
diminish  the  natural  wave  length. 

4.  The  wave  length  of  the  two  circuits  should  be  very 
nearly  the  same,  and  if  one  is  changed,  the  other  must 
also  be  changed.     In  short,  the  several  circuits  and  parts 
must  be  maintained  in  a  nice  balance  in  order  to  obtain 
the  maximum  results  and  resonance  and  this  balance  must 
be  maintained  within  the  limits  of  the  power  employed  in 
order  to  maintain  the  efficiency  of  transmission.     This 
means  that  the  small  stations  are  naturally  limited  to  small 
wave  lengths,  while  large  stations  may  be  operated  at 
longer  wave  lengths  without  appreciable  loss,  and  often 
with  gain. 

The  relations  in  the  circuit  of  fig.  18  are  very  similar 
to  those  of  fig.  17,  and  the  adjustments  are  carried  out  in 
the  same  manner.  In  fact  the  chief  difference  in  the  two 
circuits  is  in  the  matter  of  the  coupling,  and  the  effect  is 
essentially  the  same  in  other  respects. 

In  this  arrangement  the  antenna  and  condenser  cir- 
cuits include  the  primary  and  secondary  of  a  mutually  in- 


Transmitters. — Resonance.  59 

ductive  system  which  is  not  directly  connected.  The  rela- 
tive distances  between  the  two  coils  is  also  made  adjust- 
able in  practice,  so  that  the  coefficient  of  coupling  can  be 
varied.  The  chief  advantage  of  this  arrangement  is  that 
it  permits  of  sharper  tuning,  but  it  has  a  disadvantage  in 
that  this  is  accomplished  at  the  expense  of  the  intensity 
of  the  resulting  radiations. 

RESISTANCE. 

Resistance  is  an  important  item  in  a  wireless  system. 
The  high  frequency  oscillations  travel  over  the  surface  of 
a  conductor  only  and  do  not  penetrate  into  the  body  of 
the  conductor,  as  in  the  case  of  low  frequency  currents. 
Plenty  of  conducting  surface  must  therefor  be  provided 
in  both  the  condenser  and  the  inductance  coil  as  well  as 
in  all  connecting  wires  or  ribbons.  Otherwise,  a  large 
amount  of  power  is  wasted  in  heat.  Resistance  also  aids 
in  preventing  sharp  tuning,  so  that  there  is  an  added  rea- 
son for  making  all  the  parts  of  the  transmitter  of  large 
and  generous  dimensions.  A  further  desideratum  is  that 
all  of  the  circuits  as  well  as  the  several  parts,  including 
the  antenna  itself,  should  be  as  uniform  as  possible.  That 
is  the  several  conductors  should  be  as  direct  and  uniform 
as  possible,  all  joints  electrically  strong,  the  aerial  well 
insulated,  the  ground  good,  the  spark  gap  well  cooled,  and 
the  several  contacts  always  well  made.  Observance  of 
these  items  together  with  reasonable  skill  in  attuning  the 
several  circuits  is  sure  to  produce  very  satisfactory  results. 

SHARP  TUNING— BEATS. 

Reference  has  already  been  made  to  the  phenomena  of 
beats  in  a  wireless  transmitter.  Now  it  has  been  estab- 
lished, that  when  the  condenser  and  antenna  circuits  are 


60  Experimental  Wireless  Stations. 

coupled  by  either  the  direct  or  inductive  method,  that  the 
primary  or  condenser  circuit  has  two  periods  of  oscilla- 
tion instead  of  one,  and  that  the  secondary  or  antenna  cir- 
cuit has  the  same  two  periods  of  oscillation.  This  holds 
true  with  perhaps  a  few  exceptions,  in  every  case,  includ- 
ing the  ideal  coupling  of  the  two  circuits  adjusted  to  the 
same  wave  length.  As  a  result,  the  transmitter  emits  two 
distinct  waves  instead  of  one,  thereby  complicating  the 
difficulty  of  selective  receiving  from  a  field  of  stations, 
still  further.  This  is  undoubtedly  due  to  the  fact  that 
the  primary  and  secondary  circuits  are  alternately  charged 
and  discharged.  The  primary  circuit  starts  out  at  a  max- 
imum, the  secondary  gradually  building  up  while  the  pri- 
mary decreases  until  the  operation  comes  around  to  the 
beginning  of  the  cycle,  and  is  again  repeated.  The  phe- 
nomena of  beats  is  caused  in  much  the  same  manner  as 
in  sound  waves  and  the  reader  is  referred  to  an  elemen- 
tary text  on  Physics  for  a  further  understanding  of  the 
term.  The  analogy  is  complete,  when  the  electromagnetic 
waves  are  regarded  as  having  similar  properties  to  those 
of  sound  waves. 

The  experimenter  is  directly  concerned  with  this  phe- 
nomena, in  that  it  materially  concerns  the  matter  of  sharp 
tuning.  Now  when  the  transmitter  is  in  resonance,  the 
station  is  said  to  be  tuned  and  if  the  resonance  is  very 
good,  it  is  said  to  be  sharply  tuned.  This  is  the  desidera- 
tum of  real  scientific  wireless  work.  On  the  other  hand 
when  the  circuits  are  not  in  resonance,  the  station  is  said 
to  be  untuned. 

In  this  condition  the  station  is  only  a  very  little  bet- 
ter than  a  direct  untuned  station  (see  fig.  21),  and  when 
in  this  condition  a  wide  band  of  wave  lengths  are  sent  out 
which  are  difficult  to  tune  out.  Since  this  is  the  kind  of 
waves  which  have  been  largely  employed  by  amateurs, 


Transmitters. — Resonance. 


61 


it  has  brought  forth  considerable  criticism.  Even  com- 
mercial operators  have  willfully  or  innocently  used  un- 
tuned waves  or  at  least  poorly  tuned  waves  in  the  past. 
On  account  of  the  large  number  of  stations  in  operation 
at  the  present  time,  this  form  of  "pick  me  up  wave"  is  in 
disrepute  because  it  causes  unwarranted  interference.  At 
any  rate  it  is  not  scientific  or  business  like  and  is  soon  to 
be  stopped,  let  us  hope.  In  fact,  it  is  equally  or  more  im- 
portant to  have  a  sharply  tuned  station  than  to  have  one 


FIG-Et 


of  limited  wave  length  alone  without  sharp  tuning.  By 
reason  of  the  limited  wave  length,  tuning  among  experi- 
menters themselves  will  become  all  the  more  difficult  on 
account  of  the  limited  range,  and  the  sooner  all  amateurs 
install  and  operate  sharply  tuned  instruments,  the  better 
it  will  be  for  all  concerned.  To  make  this  clear,  some 
curves  submitted  to  the  radio  communication  committee 
of  the  House  of  Representatives  by  Mr.  Kolster  of  the 
Bureau  of  Standards  are  reproduced  here. 

These  curves  are  plats  to  show  the  amount  of  energy 


62 


Experimental  Wireless  Stations. 


received  under  different  conditions.  By  referring  to  Hiart 
A  the  figures,  600,  700,  800,  etc.,  at  the  bottom  indicate 
wave  length  in  meters.  The  numbers  at  the  side  of  the 
sheet  (95  to  140)  represent  the  strength  of  the  signal  re- 
ceived at  the  receiving  station.  Thus  at  600  meters,  the 


14 


700 


aoo      sco      jooo      HOO      1200 


strength  of  the  received  signal  is  105.  At  700,  it  is 
stronger,  approximately  127,  and  so  on.  The  curve  thus 
indicates  the  wave  length  and  its  corresponding  loudness 
of  the  signal.  The  signals  are  the  loudest  between  the 
wide  range  of  700  and  900  meters,  and  were  taken  from  a 


Transmitters. — Resonance. 


63 


ship  station.  The  station  is  sending  out  a  wide  band  of 
wave  lengths  (750-950  meters),  so  that  it  is  sure  to  inter- 
fere with  other  stations.  At  a  short  distance,  within, 
1,100  meters  the  current  makes  another  rise.  That  is, 
the  particular  station  under  consideration  sends  out  a  sec- 


140 


700        800        900 


1000 


1100 


ond  wave  length  defined  at  1,100  meters  as  well  as  the 
broad  band  of  700-950  meters.  This  station  is  not  send- 
ing out  any  definite  wave  length,  so  that  it  interferes  with 
all  other  stations  within  a  considerable  range.  Amateurs 
in  the  past  have  for  the  most  part  sent  out  wave  bands  of 


64 


Experimental  Wireless  Stations. 


similar  dimensions  so  that  the  meager  efforts  of  commer- 
cial operators  to  tune  out  interference  with  crude  ap- 
paratus have  been  of  little  avail. 

The  chart  1  shows  the  double  wave  length  from  an  or- 
dinary spark  excited  commercial  station,  one  wave  being 


140 


!35 


130 


125 


ISO 


THAN 
MOO 
VCR 


S  -HVTew   c 


110 


105 


100 


95 


700      fioo      900     toco 


noo 


approximately  830  meters  and  the  other  980  meters.  The 
chart  indicates  that  the  station  concerned  was  very  badly 
tuned.  As  a  contrast  to  this  chart,  the  curve  of  chart  3 
may  be  noted.  This  was  made  from  a  well  tuned  modern 


Transmitters. — Resonance.  65 

wireless  set  and  the  signals  are  sharply  defined  within  a 
range  of  75  meters.*  This  means  that  a  difference  of  75 
meters  would  entirely  cut  out  this  station  under  good  con- 
ditions. 

While  details  of  tuning  will  be  again  discussed,  it  is 
thought  that  every  reader  must  realize  the  importance  of 
sharp  tuning,  resonance,  and  definite  wave  lengths. 

DAMPING. 

The  damping  of  electromagnetic  waves  may  be  com- 
pared to  sound  waves  as  in  the  case  of  the  other  proper- 
ties. That  is,  damped  electromagnetic  waves  correspond 
to  the  sound  which  is  emitted  from  a  bell  when  a  soft  ob- 
ject such  as  the  finger  touches  it,  so  that  the  vibrations 
are  limited  or  damped.  This  is  a  common  experiment 
and  when  a  similar  property  is  understood  for  electro- 
magnetic waves,  the  term  should  not  be  difficult  to  under- 
stand. 

Undamped  waves,  then,  are  those  which  are  free  to 
vibrate  without  impedance  while  damped  waves  are  those 
which  are  more  or  less  hampered.**  Now,  absolutely  un- 
damped waves  are  practically  impossible,  but  the  nearer 
the  transmitted  waves  approach  this  point,  the  more  effi- 
cient will  be  the  transmission,  just  as  the  sound  from 
a  bell  is  greater  and  lasts  longer  if  the  bell  is  free  to 
vibrate  without  impedance.  When  the  transmitted  waves 
meet  considerable  impedance,  they  are  said  to  be  damped 
or  strongly  damped  and  in  this  condition  are  not  very 


*  Refers  to  a  Quenched  Spark  Set. 
**  Perfectly  undamped  waves  are  not  obtainable  in 
practice  but  can  be  approximated  by  using  arc  systems. 
See  Chapter  12. 


66  Experimental  Wireless  Stations. 

efficient  for  wireless  transmission.  The  damping  is  caused 
largely  by  the  resistance  which  the  circuits  offer  to  the 
oscillations  and  generally  speaking,  the  conditions  for 
undamped  waves  require  a  minimum  resistance. 

The  ordinary  spark  system  with  a  close  coupled  cir- 
cuit similar  to  that  of  fig.  17,  emits  waves  which  are  more 
or  less  damped,  depending  upon  the  adjustment,  while 
the  arrangement  of  fig.  18,  emits  waves  which  are  less 
damped,  the  other  conditions  being  practically  the  same. 
In  the  arrangement  of  fig.  18,  the  coupling  is  free,  so 
to  speak,  so  that  the  vibration  of  the  antenna  circuit  is 
not  greatly  impeded,  while  in  the  arrangement  of  fig.  17, 
the  antenna  circuit  has  a  close  coupling  with  the  condenser 
circuit  so  that  its  vibrations  are  hampered  and  limited 
to  a  considerable  extent.  Undamped  waves  or  continuous 
waves  are  a  desideratum  in  efficient  long  distance  trans- 
mission, and  it  is  for  this  reason  that  the  untuned  and  even 
the  close  coupled  circuits  are  gradually  being  superseded 
by  the  inductively  coupled  circuits  and  also  by  high  spark 
rates  instead  of  the  ordinary  spark  rates  resulting  from 
ordinary  spark  gaps.  This  matter  will  be  more  fully  dis- 
cussed later  on.  In  order  to  keep  the  damping  to  the 
smallest  possible  point,  it  is  necessary  to  keep  the  resist- 
ance of  the  circuits  down  to  a  minimum,  and  when  it  is 
remembered  that  the  resistance  of  a  conductor  to  high 
frequencies  is  greater  than  to  currents  of  low  frequencies, 
the  need  for  large  direct  conductors  should  be  all  the 
more  apparent. 


CHAPTER  V. 


PLANNING  THE  TRANSMITTER.— CALCULA- 
TION OF  WAVE  LENGTH,  CAPACITY, 
AND  CIRCUITS. 

In  planning  the  transmitter,  the  main  conditions  which 
govern  the  design  are  the  distance  over  which  the  trans- 
mission is  desired,  the  number  of  stations  and  their  loca- 
tion, to  which  it  is  desired  to  communicate,  the  local  and 
intervening  conditions,  such  as  the  condition  of  the  soil, 
atmosphere,  and  other  natural  conditions,  and  the  item 
of  expense. 

Perhaps  the  matter  of  expense  is  the  main  item  and 
it  is  always  desirable  to  keep  within  defined  limits. 
The  matter  of  expense  does  not  follow  directly  according 
to  the  transmission  distance  and  will  in  fact  vary  consid- 
erably according  to  the  conditions  in  each  case.  The 
actual  amount  depends  on  the  price  paid  for  raw  materials, 
labor,  transportation,  and  since  all  of  these  items  are  vari- 
able, the  exact  amount  must  be  figured  for  each  case. 
Thus,  if  the  raw  materials  may  be  obtained  so  that  no 
transportation  charges  have  to  be  paid,  or  if  the  apparatus 
can  be  had  second  hand,  or  if  the  labor  is  negligible,  and 
so  on,  the  cost  will  be  materially  reduced.  Ordinary  ex- 
perimental stations  do  not  entail  a  great  deal  of  expense, 
however.  While  everything  should  be  made  as  workman- 
like and  businesslike  as  possible,  extraordinary  finishes 
and  polishes  are  not  essential  to  success. 


- 
68    '  Experimental  Wireless  Stations. 

RANGE  OF  TRANSMISSION. 

While  this  cannot  be  accurately  determined  to  begin 
with,  it  may  be  approximated  to  a  sufficient  extent.  The 
experimenter  generally  has  a  few  definite  stations  with 
which  direct  communication  is  desired  and  in  all  cases 
which  permit  the  use  of  a  directive  aerial,  this  type  should 
be  adopted  for  the  purpose  specified.  When  communica- 
tion is  desired  in  all  directions,  the  umbrella  or  T  type 
aerial  will  be  the  best  to  adopt.  The  distance  to  which  a 
given  station  can  send  is  governed  largely  by  natural  con- 
ditions, such  as  character  of  the  soil,  foliage,  mountain^ 
minerals,  height  of  aerial,  and  other  similar  items,  as  well 
as  the  per  cent  of  efficiency  which  the  apparatus  is  capable 
of,  by  itself.  The  variables  are  so  great  that  while  trans- 
mission has  been  carried  out  over  a  distance  of  90  miles 
or  more  by  the  use  of  a  one  inch  spark  coil  at  an  expendi- 
ture of  perhaps  100 — 200  watts,  there  are  other  extreme 
cases  in  which  a  1  K.  W.  set  has  only  been  able  to  send 
a  few  miles.  Again,  the  same  set  will  be  able  to  send  to 
different  distances  under  different  conditions  and  at  dif- 
ferent times.  Thus,  the  transmission  in  winter  is  gen- 
erally better  than  during  the  summer,  the  transmission  at 
night  is  generally  nearly  twice  as  good  as  during  the  day 
time,  the  transmission  during  favorable  atmospheric  con- 
ditions is  from  two  to  ten  times  greater  than  when  carried 
out  under  unfavorable  atmospheric  conditions,  and  so  on. 
In  order  to  obtain  working  data,  the  working  distance 
under  practical  conditions  and  with  efficient  well  adjusted 
sets  is  taken  as  a  standard,  and,  of  course,  under  favor- 
able conditions,  this  limit  is  often  greatly  exceeded. 

This  standard  transmission  calls  for  a  range  of  ©ne 
mile  for  every  ten  watts  of  energy  which  is  used  at  the 
tmnsmittiag  station.  Tkus,  a  >£  K.  W.  (500  wa*fc$  efct 


Calculations  for  Circuits.  69 

is  expected  to  cover  50  miles,  a  J4  K.  W.  25  miles,  a  1 
K.  W.  100  miles,  and  so  on.  The  range  for  spark  coils 
will  be  similar  and  should  be  reckoned  on  the  watts  used 
instead  of  the  spark  length  alone. 

If  the  set  is  operated  under  very  favorable  conditions 
this  limit  will  generally  be  exceeded,  but  of  course,  if  the 
adjustment  or  the  instruments,  or  the  natural  conditions 
are  poor,  it  is  not  likely  that  this  limit  can  be  attained. 
With  this  basis  and  the  desired  range  known,  the  power 
required  can  be  easily  found. 

This  done,  the  question  is  limited  to  the  immediate 
selection  of  the  type  and  size  of  transformer  or  spark 
coil  to  be  used.  Since  a  transformer  requires  a  source 
of  alternating  current  such  as  a  lighting  circuit  and  since 
this  method  is  simpler  and  more  satisfactory  for  experi- 
mental purposes,  it  should  be  adopted  whenever  possible. 
Transformers  may  be  had  in  the  market  at  a  figure  which 
can  scarcely  be  duplicated  by  the  experimenter,  even  if 
his  own  time  is  not  considered,  and  the  same  may  be  said 
of  spark  coils.  The  construction  of  such  apparatus  of 
course,  affords  considerable  education  and  satisfaction, 
but  on  account  of  the  expense,  little  or  no  gain  may  be 
expected.  Very  often,  good  second  hand  coils  and  trans- 
formers may  be  had  for  little  or  nothing.  Discarded 
automobile  spark  coils  are  easily  obtained  at  garages  for 
a  mere  song  and  are  satisfactory  for  short  distances. 

There  are  two  general  types  of  transformers,  the  open 
and  closed  core  types.  The  former,  while  less  efficient 
from  the  electrical  standpoint  is  more  efficient  for  wire- 
less purposes  than  the  ordinary  closed  core  transformer. 
The  latter  type,  to  be  of  the  greatest  use  for  wireless  pur- 
poses must  be  specially  designed.  In  wireless  transmission 
the  secondary  of  the  transformer  is  largely  on  open  cir- 
cuit and  the  conditions  are  different  than  the  ordinary 


70  Experimental  Wireless  Stations. 

transformer  loads.  For  the  maximum  results,  it  is  nec- 
essary to  apportion  the  primary  and  secondary  inductance 
and  the  mutual  inductance  properly,  just  as  it  is  necessary 
to  bring  the  condenser  and  antenna  circuits  into  reso- 
nance. Almost  any  high  tension  transformer  or  spark 
coil  will  do,  of  course,  but  special  designs  are  necessary 
when  efficiency  is  desired.  In  the  ordinary  transformer, 
the  load  on  the  secondary  increases  in  practically  a  direct 
ratio  with  the  current  input,  while  in  a  wireless  station  the 
load  is  essentially  a  condenser.  This  condenser  reaches 
a  maximum  charge  only  when  the  constants  of  the  trans- 
former bear  a  resonant  relation  to  the  capacity  of  the 
condenser.  When  the  resulting  discharge  causes  a  spark, 
the  secondary  of  the  transformer  becomes  practically 
short  circuited  so  that  the  ordinary  transformer  would 
draw  a  greatly  increased  amount  of  power  and  an  arc 
would  be  formed  in  the  spark  gap.  Now  this  arc  is  very 
undesirable  since  the  condenser  cannot  be  properly 
charged  while  it  lasts  and  as  a  result  an  ordinary  trans- 
former cannot  produce  good  oscillations. 

The  wireless  transformer,  then,  must  be  designed  to 
draw  a  comparatively  small  amount  of  power  when  the 
condenser  discharges  and  short-circuits  the  secondary 
winding,  so  that  the  spark  will  extinguish  just  as  soon  as 
the  condenser  has  been  discharged. 

In  practice  this  may  be  attained  by  using  an  auxiliary 
adjustable  resistance  or  reactance  in  the  primary  circuit 
of  an  ordinary  transformer,  or  an  adjustable  inductance 
in  series  with  the  secondary  of  a  closed  core  transformer, 
or  else  by  combining  this  principle  in  the  transformer 
itself.  With  the  open  core  type  of  transformer,  an  adjust- 
able inductance  in  the  primary  circuit  becomes  essential, 
and  this  method  also  allows  of  considerable  flexibility 
in  bringing  the  transformer  into  resonance  with  different 


Calculations  for  Circuits.  71 

capacities  in  the  condenser  circuit.  Wireless  transformers 
generally  have  several  adjustments  which  allow  the  power 
input  to  be  varied  so  that  a  corresponding  change  may 
be  made  in  the  condenser  capacity  without  throwing  the 
circuit  out  of  resonance.  In  practice,  it  is  common  to  rely 
upon  the  instinct  of  the  operator  to  adjust  the  amount  of 
capacity  and  power  input  to  the  right  point  as  indicated  by 
the  appearance  of  the  resulting  spark  discharge.  The 
main  point  is  that  the  spark  in  the  gap  should  not  form 
an  arc.  With  spark  coils  this  method  must  be  largely 
used  since  an  accurate  calculation  of  the  required  capacity 
is  difficult.  Spark  coils  should  only  be  used  when  alter- 
nating current  is  not  available.  Either  batteries  or  a 
D.  C.  generator  may  be  used  to  operate  spark  coils  and 
while  they  may  be  operated  on  110  volts  A.  C.  in  con- 
nection with  an  electrolytic  interrupter,  this  method  is 
not  very  desirable.  Data  for  wireless  transformers  and 
spark  coils  will  be  found  in  Chapter  6.  The  auxiliary 
primary  apparatus  such  as  keys,  kickback  preventers,  and 
other  items  will  also  be  considered  later  since  their  design 
depends  largely  on  the  amount  of  power  used. 

After  the  power  and  source  of  power  to  be  used  have 
been  decided  upon,  the  proper  amount  of  capacity  to  be 
used  should  receive  attention  next.  This  item  depends 
on  several  quantities,  which  may  be  listed  as — 

1.  The  power  supplied  to  the  condenser.  (Watts.) 

2.  The  frequency,  or  number  of  sparks  per  second. 

3.  The  secondary  discharge  voltage. 

In  the  case  of  an  alternating  current  transformer,  the 
transformer  supplies  an  amount  of  power  to  the  con- 
denser which  may  be  represented  by  P  kilowatts.  If  the 
condenser  and  spark  gap  are  arranged  so  that  the  con- 
denser charges  to  a  sparking  potential  once  each  half- 
cycle,  or  the  natural  spark  rate,  (twice  the  natural  fre- 


72  Experimental  Wireless  Stations. 

quency.    Thus,  120  times  per  second  if  the  primary  fre- 
quency is  60  cycles), 

2 

P  =  nCV      Kilowatts 


1,000 

in  which  P  represents  the  power,  n  the  frequency  (as  60 
or  25  cycles),  C  the  capacity  of  the  condenser  in  farads, 
and  V  the  potential  in  volts  to  which  the  condenser  is 
charged  at  the  time  the  spark  begins. 

This  formula  may  be  simplified  to  the  following  form  : 
C  =  1,000  x  Power  in  K.  W. 


Now,  when  the  power,  the  number  of  cycles,  and  the 
voltage  to  which  the  condenser  is  to  be  charged,  are 
known,  the  required  capacity  can  easily  be  calculated  from 
this  formula.  It  will  be  evident  that  the  higher  the  fre- 
quency, the  less  will  be  the  needed  capacity,  so  that  for 
the  same  output,  a  smaller  capacity  may  be  used  for  60 
cycles  than  for  25  cycles,  and  so  on. 

For  example,  suppose  that  the  power  source  and 
power  conform  to  the  following  data  after  the  desired 
transmission  range  has  been  decided  as  approximately  25 
miles. 

Transformer,  J4  K.  W.,  primary  voltage  110,  fre- 
quency 60  cycles,  secondary  voltage  20,000.*  Substitut- 
ing these  values  in  the  formula 


*  This  example  serves  more  for  an  illustration  than  as 
a  typical  case. 


Calculations  for  Circuits.  73 

C  =  1,000  xj4  =     1,000  x. 25 


60  x  20,000  x  20,000  60  x  400,000,000 

.25  .0000000105  approximately 


24,000,000 

,  that  is  .0000000105  of  a  Farad. 

On  account  of  the  large  unit  represented  by  a  farad, 
wireless  capacities  are  invariably  calculated  and  carried 
out  in  microfarads,  a  microfarad  being  1,000,000th  of 
a  farad.  To  change  this  result  to  microfarads  then,  the 
answer  is  multiplied  by  1,000,000,  giving  a  result  of  .0105 
microfarads. 

This  calculation  is  very  simple  and  sufficiently  accu- 
rate for  all  ordinary  purposes.  When  the  construction 
of  condensers  for  transmitters  is  taken  up,  we  shall  see 
how  the  desired  capacity  can  be  worked  out. 

It  will  be  obvious  from  the  formula  that  when  a  low 
potential  is  used,  the  capacity  must  be  relatively  large, 
and  that  if  a  high  potential  is  used,  the  capacity  will  be 
correspondingly  small.  In  practice  the  transformer  used 
generally  has  a  potential  of  from  15,000  volts  for  J4  and 
T/2  K.  W.  to  perhaps  30,000  or  more  for  the  larger  sizes. 
However,  there  is  no  material  gain  in  the  amount  of  nec- 
essary dielectric  material  for  a  given  amount  of  power, 
whether  or  not  a  high  or  low  voltage  is  used  since  the 
small  capacity  for  a  high  voltage  is  compensated  by  the 
corresponding  increase  in  thickness  which  is  necessary  to 
withstand  the  increased  voltage  without  breaking  down. 
If  the  capacity  is  not  properly  designed,  it  is  liable  to 
break  down,  as  well  as  act  to  cut  down  the  transmitting 
efficiency  considerably.  An  increase  in  the  -frequency, 
then,  is  the  only  factor  which  will  materially  decrease 
the  actual  bulk  of  the  condenser.  Generally  speaking,  a 


74  Experimental  Wireless  Stations. 

high  voltage  within  limits  is  advantageous  for  transmit- 
ting purposes  because  of  the  resulting  transmitting  effi- 
ciency, but  this  item  should  always  be  kept  within  limits 
and  particularly  so,  when  small  and  only  moderately  in- 
sulated aerials  and  instruments  are  used. 

In  estimating  the  voltage  to  substitute  in  the  formula, 
15,000  volts  to  the  centimeter  of  spark  length  is  gener- 
ally allowed,  (1  inch  being  2.54  centimeters),  since  this 
has  been  found  the  approximate  value  for  a  heated  and 
ionized  spark  gap. 

Table  of  capacities  required  for  condenser  circuit  when 
Spark  coils  are  used. 

Length  of  spark  in  inches.  Capacity  in  microfarads 

y4  inch 001 

y2  inch 002 

1  inch 004 

2  inches 008 

3  inches 012 

4  inches 016 

These  values  are  approximate,  but  will  vary  according 

to  the  particular  coil  used.  Spark  coils  for  wireless  pur- 
poses should  be  rated  in  watts  instead  of  spark  lengths. 
Manufacturers,  please  note. 

Now,  with  the  condenser  and  transformer  decided 
upon,  the  inductance  for  the  primary  or  condenser  circuit 
is  the  next  item  to  work  out.  We  have  already  seen  how 
the  wave  length  is  varied  by  the  amount  of  inductance 
and  capacity  in  the  circuit  and  since  the  capacity  is  pre- 
ferably a  fixed  value,  (wireless  manufacturers  making 
transformers  generally  supply  a  fixed  condenser  of  the 
proper  dimensions  to  begin  with),  the  amount  of  induct- 
ance will  decide  the  wave  length  in  most  cases.  Indeed, 


Calculations  for  Circuits.  75 

when  the  condenser  is  properly  calculated  and  constructed 
the  author  believes  that  this  method  is  the  preferred 
standard.  Before  proceeding  further,  the  method  of  de- 
termining the  wave  length  must  be  understood.  This  in- 
volves only  simple  mathematics  and  can  be  easily  mastered 
by  every  reader,  if  it  is  not  already  familiar.  A  careful 
reading  together  with  the  working  of  a  few  problems  is 
all  that  is  necessary. 

CALCULATION  OF  WAVE  LENGTHS. 

The  wave  length  is  expressed  in  the  metric  system  as 
a  certain  number  of  meters  long.  Now,  feet  can  easily 
be  changed  into  meters  (sometimes  written  "Metres") 
by  dividing  the  number  of  feet  by  3.281,  (1  meter  being 
39.37  inches) .  If  the  time  comes  when  a  universal  system 
of  measurement  is  adopted,  we  will  be  saved  this  constant 
translation  from  one  system  to  another. 

The  formula  reads, 

Wave  length  (  TT)  =  v x 2it  VLC, 

(  n  )  being  a  symbol  for  wave  length,  v  the  velocity  of 
light  in  meters  =  3  x  100,000,000  in  one  second,  L=  the 
inductance  in  henrys,  and  C  =  the  capacity  in  farads.      n 
=  3.1416.  (.000001  Farad =1  microfarad.  .000001  Henry 
=  1  microhenry). 

This  formula  can  then  be  simplified  as  follows : 

Wave  length  =  300,000,000  x  2x3.1416VL.C  = 
1,884,960,000  times  the  square  root  of  the  product  of  L 
and  C.  or  1,884,960,000  times  the  square  root  of  the 
product  of  L  and  C  in  microhenrys  and  microfarads  re- 
spectively. 

Now,  for  a  given  wave  length,  the  product  of  L  and 
C  will  be  a  constant  quantity,  so  that  if  the  capacity  C  is 


76  Experimental  Wireless  Stations. 

large,  L  will  be  small,  or  if  the  inductance  L  is  large,  C 
will  be  small.  The  quantity  (LC)  varies  as  the  square 
of  the  wave  length,  so  that  if  the  wave  length  is  to  be 
doubled  (LC)  must  be  made  four  times  as  great,  or  if 
a  given  wave  length  is  to  be  tripled,  (LC)  must  be  made 
nine  times  its  original  value. 

Now,  in  the  formula  there  are  three  items  to  be  filled 
in  by  mathematical  quantities.  If  any  two  are  known, 
the  value  for  the  other  one  may  be  readily  found.  Thus, 
if  a  wave  length  of  200  meters  is  desired  with  the  use  of 
the  .0105  microfarad  condenser  already  calculated  for  the 
case  taken  as  an  illustration,  the  necessary  inductance 
can  be  readily  found.  In  order  to  still  further  simplify 
the  formula  so  that  it  will  not  be  necessary  to  extract  the 
square  root  of  (LC)  it  may  be  expressed, 

(Wave  length  \  2  __  L  x  C,  expressed  in  henrys 
1,884,960,000  /     "  and  farads  respectively. 

Using  this  formula,  and  expressing  L  and  C  in  micro- 
henry s  and  microfarads  respectively, 
200 


=  L  x  .0105 


1,884.960,000 
cancelling  and  dividing, 
1,884.960,000    )    200...  1st 
18.849,60000)    200..  2nd. 
9.424,800    )    1.  (    .1061,  quotient....  3rd 
substituting  this  simplified  value, 
(.1061)2  =  LxC  =Lx.0105  for  the  example  taken 
that  is, 

L  =  .011257  =  .011257  =  1.072  approximately 
~~C~          .0105 


Calculations  for  Circuits.  77 

that  is,  to  obtain  a  wave  length  of  200  meters  when  the 
inductance  is  an  unknown  quantity  and  the  capacity  is 
.0105  microfarads,  the  formula  gives  1.072  microhenrys 
as  the  proper  amount  of  inductance. 

Now,  this  calculation  is  very  simple,  and  may  be  used 
to  find  any  of  the  values,  wave  length,  capacity,  or  in- 
ductance, provided  the  other  two  are  known. 

It  might  be  well  to  memorize  or  jot  down  this  formula 
in  a  convenient  place,  and  if  desired  it  may  be  remem- 
bered in  the  following  form  which  applies  to  all  cases 
which  may  arise. 

/Wave   length  \2  __  ^^       Giving  C  in  microfarads  direct 
\1, 884.960,000  /  Giving  L  in  microhenrys  direct 

When  the  wave  length  is  200  this  formula  gives, 
L  x  C  —  .011257,  so  that  any  inductance  and  capacity 
which  will  give  a  product  of  .011257  when  expressed  in 
microfarads  and  microhenrys  respectively,  will  satisfy  the 
equation  and  give  a  wave  length  of  200  meters.  Now, 
since  the  condenser  is  worked  out  to  correspond  to  the 
transformer  used  in  each  case,  the  required  inductance 
can  be  found  from  the  following  for  any  case,  the  wave 
length  remaining  at  200  meters. 

L  ==  . 01 1257      /Giving  L  in  microhenrys.  \ 
C  \.C  being  in  microfarads.    J 

The  author  has  worked  out  these  simplified  values 
very  carefully  and  they  have  all  been  checked  and  re- 
checked.  It  is  believed  that  this  set  of  formulas  places 
the  calculation  of  wave  lengths  within  the  reach  of  all 
the  readers. 

When  the  construction  of  inductance  is  taken  up,  the 
matter  of  calculating  the  inductance  so  that  the  helixes 
and  transformers  are  of  the  required  design,  will  be  taken 
up. 


78  Experimental  Wireless  Stations. 

The  reader  should  have  a  pretty  good  idea  of  the  rela- 
tions of  the  circuits  to  each  other  by  now,  so  that  it  will 
be  evident  that  to  use  a  high  wave  length  of  1,500  meters, 
the  inductance  must  be  nearly  50  times  as  great  as  for  a 
wave  length  of  200  meters  with  the  same  condenser,  and 
aside  from  the  item  of  decreased  efficiency,  the  dimen- 
sions of  the  necessary  inductance  make  it  impracticable. 
Small  experimental  stations  should,  therefore,  limit  the 
wave  length  to  the  smaller  value. 

SPARK  GAP. 

Before  considering  the  secondary  or  antenna  circuit, 
a  few  notes  on  the  general  requirements  of  the  spark 
gap  will  be  given.  The  length  of  the  spark  gap  is  gov- 
erned by  the  potential  at  the  terminals,  so  that  it  must 
be  increased  as  the  potential  at  which  the  condenser  is 
charged  is  increased,  the  other  conditions  being  constant. 
The  other  dimension,  or  the  size  of  the  faces  of  the  spark 
electrodes,  must  be  sufficient  to  conduct  the  energy  with- 
out undue  heating.  These  are  the  essential  features  of 
a  gap  and  the  exact  size  and  shape  admits  of  numerous 
variations.  Suitable  constructions  for  various  types  of 
gaps  will  be  taken  up  in  detail  later. 

ANTENNA  CIRCUIT. 

The  proper  dimensions  for  the  antenna  circuit  are 
obtained  in  much  the  same  manner  as  for  the  condenser 
circuit,  and  both  of  the  said  circuits  must  be  adjusted  to 
very  nearly  the  same  wave  length  for  the  maximum  re- 
sult. There  is  some  difficulty  in  calculating  the  capacity 
and  inductance  of  an  antenna  with  any  degree  of  accu- 
racy, since  there  are  many  elusive  quantities  which  make 
up  the  total.  When  the  primary  or  condenser  circuit  is 


Calculations  for  Circuits.  79 

accurately  calculated  and  adjusted,  the  antenna  or  sec- 
ondary circuit  can  probably  be  best  adjusted  to  resonance 
with  the  primary  circuit  by  means  of  a  hot  wire  ammeter, 
wave  meter,  geissler  tube,  or  miniature  light  bulb,  and 
some  of  these  methods  will  be  taken  up  in  detail  later. 

The  capacity  of  the  antenna  wires  increases  with  the 
height,  but  not  directly.  It  is  nevertheless  desirable  to 
have  the  aerial  as  high  up  as  is  possible.  The  capacity 
of  stranded  wire  is  only  a  very  little  greater  than  that  of 
a  solid  conductor  having  the  same  outside  circumference. 
The  capacity  of  a  number  of  wires  in  close  proximity  is 
considerably  less  than  the  sum  of  the  individual  capaci- 
ties. Solid  metallic  structures  in  space  have  only  a  very 
little  greater  capacity  than  ordinary  wires,  and  a  few 
small  wires  uniformly  spaced  have  practically  as  great  a 
capacity  as  a  solid  sheet  or  tube  occupying  a  similar 
space.  The  use  of  sheets,  netting,  tubing,  and  the  like  is 
therefore  not  economical  or  desirable.  The  approximate 
inductance  and  capacity  of  aerial  wires  can  be  worked  out 
by  a  complicated  process,  but  since  even  this  method 
admits  of  considerable  error,  these  formulas  are  omitted. 

Perhaps  the  most  simple  and  satisfactory  method  of 
apportioning  the  antenna  conductors  for  a  given  set  is  as 
follows:  Take  three- fourths  of  the  wave  length  in 
meters  to  find  the  wave  length  to  be  embodied  in  the  an- 
tenna conductors.  That  is,  make  the  natural  wave  length 
of  the  antenna  approximately  three-fourths  of  the  total 
wave  length.  To  do  this,  it  is  necessary  to  make  the 
effective  length  of  the  aerial  approximately  .6  of,  the  total 
wave  length  in  meters,  in  feet.  This  is  calculated  by  a 
process  which  is  simple  and  of  no  direct  interest,  and 
to  illustrate, — 


80  Experimental  Wireless  Stations. 

For  a  wave  length  of  200  meters,  the  effective  length 
of  the  aerial  should  be  .6  of  200  in  feet,  or  120  feet.  (See 
Aerials.)  This  is  only  a  rough  approximation,  however. 
For  large  wave  lengths,  this  method  is  not  recommended. 
When  this  method  is  used,  a  margin  of  approximately 
one-fourth  of  the  total  wave  length  is  left  to  the  adjust- 
ment of  the  secondary  portion  of  the  oscillation  trans- 
former. In  constructing  the  aerial  itself,  it  is  well  to 
allow  one  No.  12  conductor  or  its  equivalent  in  the  an- 
tenna for  every  100  watts  of  energy  to  be  used,  and  to 
provide  a  minimum  of  two  conductors  even  if  only  30 
watts  are  to  be  used.  Thus,  a  ^2  K.  W.  set  should  have 
five  antenna  conductors  at  least,  and  so  on.  In  fact  the 
limit  is  soon  reached  so  that  it  is  impracticable  to  use 
more  than  three-fourths  or  one  K.  W.  with  a  wave  length 
of  200  meters  or  less.  For  one  K.  W.  and  larger  sets,  a 
high  wave  length  should  be  planned  for.  This  will  mean 
a  considerable  increase  in  the  total  expense,  as  everything 
is  best  enlarged  accordingly.  (See  Chapter  19  for  legal 
requirements.)  A  }4  or  ^  K.  W.  outfit  is  ideal  for 
experimental  purposes. 

We  have  now  considered  the  main  factors  of  the  trans- 
mitting set  and  station,  and  the  details  are  ready  for  at- 
tention. In  choosing  a  site  for  a  station,  a  quiet  place 
is  to  be  preferred  and  this  matter  is  particularly  true  of 
the  operating  room.  The  latter  should  be  provided  with 
good  ventilation,  sound,  tight  walls,  and  should  have  a 
total  floor  space  of  about  125  square  feet  if  possible, 
though  less  may  be  used.  A  corner  of  a  workshop,  fab- 
oratory,  or  similar  ready  made  place  is  suitable. 

Note :  It  should  be  remarked  that  the  estimated  range 
of  one  mile  for  every  ten  watts  can  not  be  expected  over 
long  distances  with  short  aerials  and  wave  lengths  on 
atsoouitt  oC  tfce  abaorbtkm  of  short  waves. 


CHAPTER  VI. 


TRANSFORMERS.  SPARK  COILS. 

Transformers  for  wireless  purposes  are  relatively  in- 
expensive and  quite  efficient.  They  are  rated  according 
to  the  power,  as  J4  K.  W.,  l/2  K.  W.  and  so  on.  They 
can  only  be  used  when  an  alternating  current  supply  is 
available.  For  experimental  purposes  a  transformer  giv- 
ing a  secondary  potential  of  15,000  or  20,000  volts  and 
of  J4  or  1/2  K.  W.  is  recommended,  preferably  the  for- 
mer. The  reader  is  advised  that  it  will  probably  cost 
as  much  to  construct  a  suitable  transformer  as  to  buy  it 
in  the  open  market  and  that  some  skill  is  required  in 
addition  to  the  data  here  given  if  an  efficient  transformer 
is  to  be  constructed. 

In  its  simplest  form,  a  transformer  is  nothing  more 
than  two  independent  coils  of  wire  wound  around  a  com- 
mon iron  core.  An  alternating  current  impressed  upon 
one  of  the  coils  (the  primary)  causes  a  current  to  be 
generated  in  the  other  coil  by  mutual  induction,  although 
the  two  coils  are  insulated  from  each  other  and  the  core. 
The  second  coil  is  called  the  secondary  and  is  generally 
wound  for  wireless  purposes  so  that  it  has  a  large  num- 
ber of  turns.  The  voltage  of  the  primary  and  the  voltage 
of  the  secondary  have  a  ratio  corresponding  to  the  rela- 
tive number  of  turns  and  a  corresponding  amperage. 
Thus,  if  the  primary  has  100  turns  and  is  supplied  with 
a  voltage  of  100  and  current  of  10  amperes,  (IK.  W.), 
and  the  secondary  has  50,000  turns  of  wire,  the  secondary 
voltage  will  be  50,000,  but  the  amperage  will  only  be  one- 


82  Experimental  Wireless  Stations. 

fiftieth  of  an  ampere.*  Now,  there  are  many  quantities 
to  consider  in  designing  a  transformer,  and  a  desired 
design  can  be  nicely  calculated.  However,  in  order  to 
cover  the  most  ground  in  the  least  space,  the  matter  in 
this  chapter  will  be  limited  to  the  direct  construction  of 
designs  which  have  already  been  worked  out  as  suitable. 

The  core  is  generally  arranged  in  the  form  of  a  rect- 
angle and  is  made  up  of  thin  laminations  of  soft  sheet 
iron,  each  lamination  being  coated  on  one  side  with  var- 
nish for  insulation.  This  is  to  prevent  eddy  current  loss 
and  is  essential.  The  arrangement  of  the  coils  admits  of 
many  variations,  but  for  simplicity  of  construction  it  is 
preferable  to  place  the  primary  winding  on  one  leg  of 
the  core  and  the  secondary  on  an  opposite  leg.  The  flux 
leakage  is  somewhat  greater  than  when  the  primary  and 
secondary  are  evenly  divided  on  the  two  cores,  but  the 
construction  and  particularly  the  insulation  is  facilitated 
by  this  method.  The  foremost  requirement  of  wireless 
transformers  is  good  insulation,  and  this  item  should 
receive  particular  attention  in  the  construction. 

The  following  data  will  be  found  useful  in  construct- 
ing suitable  transformers  (closed  core  type),  with  out- 
puts which  compare  favorably  with  the  inputs.  The  con- 
struction must  be  carefully  carried  out  or  the  dimensions 
and  sizes  will  not  hold  good.  This  data  is  for  transfor- 
mers operating  on  60  cycles  at  a  voltage  of  100  to  120, 
which  is  the  current  most  in  use.  The  cores  are  arranged 
in  the  form  of  a  rectangle  and  the  primary  is  placed  on 
one  leg,  while  the  secondary  is  placed  on  the  other.  These 
legs  are  denoted  by  the  letter  B  in  the  table.  The  letter 


*  This  is  taken  without  considering  the  core  and  cop- 
per losses.  Good  wireless  transformers  are  about  90  per 
cent  efficient. 


Transformers.    Spark  Coils. 


83 


TABLE  OF  TRANSFORMER  DATA.* 


Wattsj    100 

250 

500 

750 

1000 

1500 

2000 

A 

9 

9y2 

9l/2 

9l/2 

11 

12 

11 

B 

6^ 

7 

7            7y2         10 

10 

IS 

C 

\y2 

\y$ 

1^         124          2              2^ 

2l/2 

D 

16 

12 

14           13              6 

5 
854 

_4 

E 

5 

5/^ 

5^         5j4          6l/2 

F 

3/16 

T/ 

l/4          54            54            54 

54 

G 

Empire  Cloth 

H 

16 
D.C.C. 

16 
D.C.C. 

14 
D.C.C. 

14 
D.C.C. 

12 
D.C.C. 

10 

D.C.C. 

8 
D.C.C. 

J 

Zl/2 

4 

Sl/2 

6 

7 

10 

14 

K 

8 

9 

9 

10 

18 

22 

23 

L 

34  Enamel 

32  Enamel       |  30  En'l 

M 

2l/2 

2/2 

2y2 

2H 

5 

5        1      9 

N 

1A 

y* 

% 

% 

54           54 

54 

O 

*A 

1A 

l/4 

l/4 

54           54 

54 

P 

7 

7 

7 

8 

10 

10 

16 

Q 

V* 

54 

1A 

54 

54           54 

54 

R 

Empire  Cloth. 

Key  to  Table. 

A — Length  of  Core  (outside  measurement). 

B— Width  of  Core  (outside  measurement). 

C — Thickness  of  Core. 

D — Number  of  primary  layers. 

E — Width  of  secondary  sections  (each  side). 

F — Thickness  of  insulation  between  core  and  primary. 

G — Kind  of  insulation  between  core  and  primary. 

H — Size  (B  and  S)  primary  wire. 

J — Weight  of  primary  wire. 

K — Approximate  number  of  pounds  secondary  wire. 

L — Size  (B  and  S)  secondary  wire. 

M — Length  of  windings. 

N — Thickness  of  separators  for  secondary  sections. 

O — Thickness  of  sections  in  secondary. 

P — Number  of  sections  in  secondary. 

Q — Thickness  of  insulation  between  core  and  secondary. 

R — Kind  of  insulation  between  core  and  secondary. 


Popular  Electricity. 


84 


Experimental  Wireless  Stations. 


C  denotes  one  side  of  the  core.  The  core  proper  is  square, 
so  that  when  the  thickness  is  given  as  2  inches,  it  means 
that  the  core  is  2x2  inches.  The  separators  (N)  are  of 
the  proper  size  when  fibre  is  used. 

CONSTRUCTIONAL  DETAILS. 

The  core.  Fig.  22  shows  the  arrangement  of  a  square 
core  and  details.  The  strips  are  best  cut  out  by  means 
of  square  shears  which  may  be  found  at  any  hardware 


RE. 


or  tinshop.  When  this  type  of  core  is  used,  it  will  be 
necessary  to  use  an  auxiliary  primary  inductance  or 
reactance  coil  in  order  to  compensate  for  the  capacity 
and  maintain  a  high  power  factor.  This  type  of  trans- 
former lacks  sufficient  inductance  after  the  windings  are 


Transformers.    Spark  Coils. 


85 


in  place,  so  the  arrangement  of  fig.  23  should  be  adopted 
if  possible.*  This  form  of  core  gives  rise  to  considerable 
magnetic  leakage,  causing  an  increase  in  the  primary  in- 
ductance, and  makes  the  use  of  auxiliary  inductance  un- 
necessary. When  the  primary  has  insufficient  inductance 


FIG.S3. 


the  spark  forms  an  undesirable  arc  at  the  gap,  so  that 
this  is  an  important  item.  In  some  types  of  wireless 
transformers,  this  extra  portion  or  tongue  is  made  so 
that  the  air  gap  is  adjustable,  giving  a  close  control  of 
the  current.  This  extra  portion  does  not  materially  alter 
the  dimensions  given  in  the  table,  but  extra  iron  must  be 
allowed  and  calculated  if  this  arrangement  is  adopted. 
Transformer  iron  may  be  had  from  supply  houses  cut 
to  size,  or  a  good  grade  of  stovepipe  iron  may  be  used. 


*  Extra  iron  must  be  allowed  as  the  table  is  for  plain 
cores. 


86  Experimental  Wireless  Stations. 

The  legs  should  be  wound  with  a  few  layers  of  empire 
cloth.  The  core  can  be  squared  up  by  tapping  it  with 
a  hammer  or  mallet.  The  secondary  leg  should  be  fur- 
ther insulated  by  additional  turns  of  empire  cloth,  the 
number  of  which  should  be  ample  to  take  care  of  the 
estimated  secondary  voltage  and  a  50  per  cent  overload. 
No.  6  is  a  convenient  size  for  the  empire  cloth  and  has 
an  average  puncture  voltage  of  7,800.  A  good  way  to 
find  the  desired  number  of  turns  is  to  use  as  many  times 
the  number  of  turns  used  for  the  primary  leg  as  the  num- 
ber of  secondary  turns  is  times  the  number  of  primary 
turns,  that  is,  the  insulation  is  best  proportioned  accord- 
ing to  the  relative  turns  of  the  two  windings. 

The  Primary.  Wind  the  primary  evenly  on  the  pri- 
mary leg,  leaving  some  6  or  10  inches  at  the  ends  of  the 
wire  for  leads.  Taps  may  be  taken  out  towards  the  end, 
if  different  inputs  are  desired,  in  which  case  the  number 
of  primary  turns  should  be  slightly  increased  over  the 
number  given  in  the  table.  The  winding  is  best  done  by 
hand  on  account  of  the  heavy  wire  and  should  never  ap- 
proach too  near  to  the  part  of  the  core  which  forms  a 
joint,  or  beyond  the  empire  cloth,  it  being  understood  that 
the  latter  is  kept  within  the  limits  of  the  leg  proper.  The 
completed  winding  can  be  covered  with  a  few  turns  of 
empire  cloth  or  tape. 

The  Secondary.  The  sections  are  wound  on  a  section 
former  in  a  lathe  or  makeshift  lathe.  The  arrangement 
of  a  section  winder  is  shown  in  fig.  24,  and  should  be 
made  in  proportion  to  the  size  of  the  coil  to  be  wound. 
This  former  should  be  made  from  iron,  steel,  or  brass 
and  not  of  wood,  and  is  preferably  made  by  a  machinist 
so  that  the  plates  are  true.  The  saw  cuts  (slots)  are  to 
allow  threads  to  be  passed  around  the  completed  section 
before  it  is  removed.  This  round  form  is  more  con- 


Transformers.    Spark  Coils. 


87 


venient  than  a  square  former,  although  the  latter  may  be 
used.  The  resulting  air  space  is  no  disadvantage  since  it 
acts  as  a  cooling  duct.  The  winding  should  be  done  slow- 
ly and  evenly,  avoiding  kinks  and  breaks.  A  broken  wire 
should  be  soldered. 

With  a  little  practice  this  winding  will  not  be  diffi- 
cult, and  can  be  rapidly  carried  out.     The  section  should 


Slots 


^.       FIB.  5-4 


P.£. 


be  tightly  wound  and  when  completed,  the  threads  should 
be  passed  around  it  and  through  the  slots  to  keep  it  in 
shape.  Leave  several  inches  at  the  beginning  and  end 
of  the  winding  for  connections.  After  it  is  bound,  the 
section  should  be  removed  with  care  and  placed  into  a 
pot  or  pan  containing  melted  paraffine  or  a  mixture  of 
paraffine  and  beeswax.  The  later  should  not  be  too  hot 
since  its  insulating  value  is  less  if  it  is  at  too  high  a 
temperature.  Let  the  section  soak  in  the  wax  for  some 
time  until  air  bubbles  cease  to  rise,  then  lift  it  out  by 
means  of  a  string  or  spoon.  Place  the  section  on  a  porce- 
lain plate  and  squeeze  the  excess  wax  out  by  pressing 


88  Experimental  Wireless  Stations. 

on  the  section  from  the  top  with  another  cold  porcelain 
plate.*  The  other  sections  can  be  wound  while  the  first 
few  are  being  insulated,  to  save  time.  These  sections 
can  be  taped  with  a  strip  cut  from  empire  cloth  if  de- 
sired. The  fibre  separators  can  also  be  soaked  in  the  wax 
mixture. 

Assembling.  The  sections  should  be  connected  in 
series  so  that  they  form  a  consecutive  winding  with  the 
connections  made  alternately  at  the  middle  and  at  the  out- 
side. The  joints  should  be  soldered.  Be  sure  that  the 
sections  are  properly  connected  so  that  the  direction  of 
the  winding  is  consecutive  as  otherwise  one  or  more  sec- 
tions will  buck  up  against  the  rest.  The  sections  should 
then  be  arranged  on  the  core  with  the  separators  between 
them,  and  melted  wax  may  be  used  to  fill  up  the  inter- 
vening space  so  that  they  will  be  rigidly  in  place  on  the 
core.  It  is  good  practice  to  divide  the  insulation  between 
the  sections  into  two  parts  so  that  the  inner  connection 
can  be  placed  between  two  separators.  The  sections  are 
best  joined  after  they  are  arranged  on  the  core.  A  num- 
ber of  separators  should  be  placed  at  each  end  of  the 
completed  winding  and  if  possible  a  thick  head  should 
be  provided  as  a  flange  for  each  end  of  the  coil. 

The  primary  and  secondary  legs  are  now  joined  by 
the  core  pieces  and  squared  up.  The  tongue  of  the 
tongue  type  is  left  alone  for  the  present.  In  the  tongue 
type,  the  primary  core  is  placed  at  the  tongue  end.  This 
tongue  should  be  nicely  bound  by  itself.  The  core  is  then 
clamped  together  and  nicely  squared  up  by  means  of 
strap  or  angle  iron  and  bolts. 

The  transformer  can  now  be  mounted  in  any  suitable 
manner  and  the  terminals  brought  out  to  suitable  binding 


*  Glass  may  also  be  used 


Transformers.    Spark  Coils.  89 

posts.  The  tongue  is  left  in  an  adjustable  position  close 
to  the  core  but  insulated  therefrom,  so  that  its  relative 
distance  can  be  adjusted  according  to  the  amount  of  con- 
denser used  across  the  secondary  terminals.  Tests  should 
be  made  with  a  telephone  receiver  and  battery  for  short 
circuits,  for  breaks  and  if  any  are  found  they  must  be 
located  and  repaired.  It  is  well  to  cover  the  secondary 
with  a  number  of  layers  of  empire  cloth.  The  other  de- 
tails are  left  to  the  reader. 

REACTANCE  COIL. 

A  suitable  reactance  coil  for  use  with  the  transfor- 
mer when  a  plain  core  type  is  employed,  may  be  con- 
structed by  making  a  hollow  coil  of  wire  and  sliding  an 
;ron  core  in  or  out  of  it  according  to  the  desired  adjust- 
ment. The  core  should  be  of  sheet  iron  and  of  dimen- 
sions corresponding  to  the  size  of  the  primary  leg  of 
the  transformer  core.  That  is,  if  the  primary  leg  is 
10  inches  long,  and  2x2  inches,  the  core  for  the  reactance 
should  be  this  same  size  or  a  little  larger.  Now  make  a 
wooden  or  fibre  frame  about  one-eighth  or  three-six- 
teenths of  an  inch  thick  with  inside  dimensions  so  that 
the  iron  core  can  slide  freely  in  and  out  of  it,  and  wind 
about  two  or  three  layers  of  wire  on  it.  The  wire  should 
be  a  few  sizes  larger  than  the  primary  wire,  if  possible. 
Thus,  if  the  primary  wire  is  No.  12,  No.  10  is  suitable 
for  the  reactance  coil.  This  reactance  is  connected  in 
series  with  the  primary  winding  and  the  adjustment  is 
made  by  putting  more  or  less  of  the  iron  core  inside  of 
the  winding. 

It  is  believed  '"hat  the  foregoing  will  be  sufficient  work- 
ing directions  to  enable  the  reader  to  construct  efficient 
transformers  and  reactances,  provided  that  the  work  is 


90  Experimental  Wireless  Stations. 

carefully  carried  out.  Many  minor  details  have  been 
omitted,  and  unless  the  reader  has  some  experience,  he 
will  very  likely  find  several  little  points  which  must  be 
independently  solved.  The  main  requisite  is  again  stated 
to  be,  INSULATION. 

Inasmuch  as  open  core  transformers  are  less  efficient 
than  closed  core  types  and  little  if  any  easier  or  cheaper 
to  construct,  designs  for  this  type  are  omitted. 

SPARK  COILS. 

A  spark  coil  is  similar  to  a  transformer  except  that 
it  has  an  open  core  and  operates  by  means  of  an  inter- 
rupted current.  These  coils  are  preferably  purchased, 
since  they  may  be  had  almost  as  cheap  as  the  materials 
for  construction.  However,  for  those  who  may  wish  to 
construct  coils  and  who  have  some  idea  of  the  details, 
the  following  data  for  wireless  coils  is  given.  Wireless 
coils  require  a  different  design  than  ordinary  spark  coils. 
The  sections  may  be  wound  as  has  already  been  de- 
scribed for  transformer  sections.  The  core  in  this  kind 
of  coil  is  made  up  of  a  bundle  of  straight  soft  iron  wires, 
which  may  be  had  cut  to  size  from  supply  houses.  The 
other  requirements,  such  as  insulation,  etc.,  are  similar  to 
those  for  transformers,  and  with  the  aid  of  the  diagram 
of  the  relations  of  the  circuits  shown  in  fig.  25,  it  is  not 
thought  that  there  will  be  any  difficulty  in  carrying  out 
the  construction.  The  vibrator  is  best  purchased  from  a 
supply  house,  since  it  is  as  cheap  or  cheaper  than  making 
one.  The  construction  of  the  condenser  is  similar  to  the 
construction  used  in  receiving  condensers,  and  the  reader 
is  referred  to  this  heading  for  further  instructions. 


Transformers.    Spark  Coils.  91 


TABLE 

FOR 

WIRELESS 

SPARK 

COILS. 

(Size.) 

A. 

B. 

C. 

D. 

E. 

F. 

G. 

1A  in. 

5/2 

/2 

CT 

1-16 

in.      20 

225 

Em. 

Y-2.  in. 

5/2 

/2 

CT 

1-16 

in.      20 

225 

Em. 

1  in. 

5^4 

/2 

Em 

2 

18 

170 

Em. 

2  in. 

7 

N 

Em 

2 

16 

184 

Em. 

3  in. 

8 

?4 

Em 

2 

16 

208 

Em. 

4  in. 

8^4 

i 

Em 

3 

16 

232 

Em. 

5  in. 

9/2 

i 

Em 

3 

16 

256 

Em. 

6  in. 

10 

1/4 

Em 

3 

14 

214 

Ml 

8  in. 

14 

1/2 

Em 

3 

14 

320 

Ml 

10  in. 

24 

3 

Em 

4 

12 

400 

Ml 

(Size.) 

H. 

I. 

j. 

K. 

L. 

M. 

N. 

M  in. 

4 

38 

3  oz. 

1 

\y% 

4J4 

250 

/  in. 

4 

38 

4  oz. 

1 

1/8 

4J4 

300 

1  in. 

6 

38 

H  lb. 

2 

124 

4/2 

800 

2  in. 

6 

36* 

1  lb. 

2 

2J4 

5J4 

1400 

3  in. 

8 

36* 

\y2  ib. 

2 

3 

6 

2000 

4  in. 

8 

36* 

2  lb. 

3 

4 

6 

2500 

5  in. 

8 

36* 

3  lb. 

3 

4J4 

6 

3800 

6  in. 

H  in. 

36* 

5  lb. 

4 

5 

6J^ 

6000 

8  in. 

>6in. 

36* 

8  lb. 

8 

8 

7 

8500 

10  in. 

j6in. 

28* 

12  lb. 

16 

11 

12 

10,500 

IN  THIS  TABLE,— 

A — Length  of  Core  In  inches. 

B — Diameter  of  Core  in  inches. 

C — Insulation  on  Core — (C.  T. — Carboard  tube,  E.  M. — Empire 
Cloth.) 

D — Thickness  of  insulation  on  core. 

(In  layers,  except  V\  inch  and  %  inch  sizes.) 

E— Size  (B&S)  Primary  Wire  (D.  C.  C.) 

F — Number  Turns  Primary  Wire. 

G — Kind  of  insulating  tube. 

(Em — Empire  Cloth)    (Mi — Micanite.) 

H — Thickness  Insulating  Tube.     (Layers  for  Em.  and  inches 
for  Mi.) 

I — Size  (B&S)  Secondary  Wire.      (*  means  Enameled.) 

J — No.  Pounds  Secondary  Wire. 

K — No.  Sections  in  Secondary. 

L — Approximate  Diameter,  Secondary.      (In  inches.) 

M — Distance  between  coil  heads.      (In  inches.) 

N — Total  No.  Sq.  In.  of  Foil  in  Condenser. 

Note:  These  coils  use  a  medium  speed  vibrator.  To  use  table, 
find  length  of  spark  wanted  (Size)  and  read  across,  as  %  inch — 
5% — % — C.  T.  etc.,  %  inch — 4 — 38 — 3  oz.  etc. — Adapted  from  Pop. 
Electricity. 


92 


Experimental  Wireless  Stations. 


A  transformer  is  to  be  preferred  and  should  be  used 
whenever  possible.  The  spark  coil  will  operate  satis- 
factorily on  one  or  two  six  volt  storage  cells.  A  spark 


coil  may  also  be  used  with  an  electrolytic  interrupter  on 
1 10  volt  A.  C.  or  D.  C.  current.     (See  Chapter  7. ) 


CHAPTER  VIL 


AUXILIARY    APPARATUS.     KEYS,    ELECTRO- 
LYTIC INTERRUPTER,  KICKBACK  PRE- 
VENTION, AERIAL  SWITCHES. 


ELECTROLYTIC  INTERRUPTER. 

By  using  an  electrolytic  interrupter,  a  spark  coil  can 
be  operated  on  110  V.  A.  C.  or  D.  C.     The  author  finds 


Outtt «Ur 


e 


FIG. SB. 


PE. 


after  numerous  trials  that  the  interrupter  shown  in  fig.  26 
is  the  most  serviceable  for  experimental  purposes.  This 
interrupter  is  very  inexpensive  and  such  common  things 
as  mason  or  other  jars  may  be  utilized.  The  electrodes 
can  be  either  brass  or  lead,  preferably  the  latter.  The 
electrolyte  is  made  up  by  adding  a  little  sulphuric  acid 
to  water,  or  else  by  adding  some  sal  ammoniac  to  water. 
Other  salts  may  also  be  used,  but  common  table  salt  is 
not  suitable.  The  proper  amount  is  found  by  experi- 


94 


Experimental  Wireless  Stations. 


ment.  It  is  advisable  to  use  the  cooling  jar  as  shown, 
as  the  interrupter  heats  rapidly  when  in  use.  The  only 
difficulty  in  construction  will  probably  be  the  hole  in  the 
glass  or  porcelain,  or  clay  (glazed)  jar.  This  may  be 
readily  bored  with  a  new  sharp  twist  drill,  using  turpen- 
tine as  a  lubricant.  The  glazed  clay  is  the  easiest  to 
bore.  The  hole  should  not  be  too  large,  or  too  much 
current  will  pass.  The  following  sizes  for  the  holes  are 
suitable. 

1-32  inch  for  coils  giving  up  to  %  inch  spark. 

1-16  inch  for  coils  giving  up  to  2  inch  sparks. 

3-32  inch  for  coils  giving  up  to  3  inch  sparks. 

1-8  inch,  largest  size  advised.  This  size  allows  from 
5  to  8  amperes  to  pass. 


*K 


FIG.S7. 


In  using  the  interrupter,  the  vibrator  contacts  of  the 
coil  must  be  screwed  down  tight  as  the  vibrator  is  not 
needed.  The  interrupter  is  connected  in  series  with  the 
coil.  (See  fig.  27.)  The  interruptions  will  be  faster  with 
the  smaller  size  hole  other  conditions  being  the  same,  and 
they  depend  upon  the  fact  that  a  gaseous  insulating  film 
is  generated  at  the  point  of  contact  by  the  current  which 
temporarily  breaks  the  current.  The  interruptions  or 
makes  and  breaks  occur  at  a  high  rate  of  speed.  The 


Auxiliary  Apparatus. 


95 


interruptions  can  be  regulated  to  some  extent  by  means  of 
a  variable  inductance  in  series  with  it  and  the  coil.  This 
may  be  constructed  like  the  reactance  coil  described  in 
Chapter  6. 

KICKBACK  PREVENTION. 

In  using  transformers  or  coils  and  interrupters  con- 
nected to  lighting  circuits,  the  high  tension  currents  often 
kick  back  into  the  line  and  cause  considerable  damage. 
The  common  effect  of  kickbacks  are  punctured  meters, 
arcs  in  electric  light  fixtures,  short  circuits  and  blown 


To  MeT 


'Fuses 


Tj-o«sf««-n»«r. 


FIG.EQ. 


fuses.  In  fact,  whenever  more  than  200  watts  are  drawn 
from  the  line  to  operate  a  coil  or  transformer,  steps 
should  be  taken  to  prevent  kickbacks.  An  efficient  triple 
preventer  is  shown  in  fig.  28.  The  protection  is  three- 
fold, ground  dissipators  being  provided  in  the  form  of 
condensers,  high  resistances,  and  minute  gaps.  These  are 
all  connected  across  the  terminals  of  the  line  supplying 
current  to  the  primary  of  the  coil  or  transformer.  The 
gaps  should  be  very  carefully  made  so  that  they  do  not 
touch  each  other  by  a  minute  distance.  The  condenser 
should  have  a  large  capacity  and  may  be  of  the  following 
dimensions  or  their  equivalent. 


96  Experimental  Wireless  Stations. 

Each  condenser  has  ten  plates  of  8x10  glass,*  between 
which  are  sheets  of  tinfoil  6x8  inches  alternately  con- 
nected to  form  a  capacity.  This  is  constructed  like  any 
other  condenser. 

The  high  resistance  is  attained  by  using  graphite  rods, 
each  having  about  1,000  ohms  resistance,  and  should  be 
of  large  diameter  to  dissipate  the  heat  which  is  accumu- 
lated after  a  time.  These  rods  are  also  connected  directly 
across  the  line.  The  ground  may  be  the  regular  ground 
of  the  station  or  else  the  lighting  ground  may  be  conve- 
niently used.  This  arrangement  will  take  care  of  kick- 
backs and  will  save  the  remainder  of  the  circuits  from 
damage.  The  fuses  shown  are  6  amp.  plug  fuses,  and 
should  be  promptly  renewed  if  they  blow.  This  arrange- 
ment may  mean  the  difference  between  a  serious  fire  and 
constant  freedom  from  injury  or  trouble  and  should  be 
adopted.  The  condenser  cares  for  ordinary  small  charges, 
the  gap  for  excessive  charges,  and  the  rods  are  an  addi- 
tional protection  for  the  meter.  The  latter  can  be  dis- 
pensed with  if  desired. 

KEYS. 

The  key  used  for  breaking  the  current  into  dots  and 
dashes  must  handle  considerable  currents  in  most  cases 
and  ordinary  telegraphy  keys  are  only  suited  when  a  few 
watts  are  used,  as  with  small  spark  coils.  The  reader 
can  easily  construct  a  heavy  key  along  the  lines  of  a 
telegraph  key,  using  large  pieces  of  zinc  or  two  silver 
dimes  for  contacts.  An  attachment  for  an  ordinary  tele- 
graph key  which  will  handle  large  currents  is  shown  in 
fig.  29.  The  regular  contacts  are  not  used  with  this  ar- 


Heavy  paraffined  paper  can  be  used. 


Auxiliary  Apparatus. 


97 


rangement.  A  similar  arrangement  can  easily  be  con- 
structed. The  arrangement  is  so  simple  that  further 
comment  seems  unnecessary.  The  contacts  can  be  of  zinc 


B«f)t  Bui* 

$tri> 


FIG. 


or  silver  and  should  be  of  large  surface.  The  distance 
between  the  contacts  can  be  adjusted  as  shown.  The  aver- 
age telegraph  key  will  have  to  be  mounted  on  a  separate 
base  to  use  this  arrangement.  A  similar  set  of  contacts 
can  be  magnetically  operated  as  shown  in  fig.  30,  in  which 


piv«t 


FIE  3D 


.     f.E. 


case  an  ordinary  telegraph  or  strap  key  can  be  used  to 
close  the  circuit.  This  arrangement  is  advisable  when 
currents  in  excess  o  f  10  amperes  must  be  handled.  Springy 
metal  can  be  substituted  for  the  mercury. 


98 


Experimental  Wireless  Stations. 


Another  arrangement  for  handling  large  currents  is 
shown  in  fig.  31.  Other  arrangements  for  the  same  pur- 
pose are  to  connect  a  large  condenser  in  shunt  around 
the  key  contacts  to  absorb  the  spark,  and  to  use  oil  about 
the  contacts  to  prevent  arcs  from  forming.  The  magnets 
shown  in  the  figure  may  be  either  single  or  double  pole 
and  of  any  suitable  dimensions.  The  essential  feature  is 
that  the  poles  should  be  extended  to  the  locality  of  the 
contacts,  so  that  they  can  act  to  blow  out  arcs  which  form 
before  the  latter  become  of  unwieldly  proportions.  Note 


-jPole  fYtCCS 


Fic.ai. 


the  connections.     Strap  iron  is  suitable  for  the  pole  ex- 
tensions. 

AERIAL  SWITCHES. 

There  are  many  forms  of  aerial  switches,  the  object 
of  which  is  to  change  from  the  sending  to  the  receiving 
instruments.  For  small  stations,  an  ordinary  double  or 
triple  pole  double  throw  switch  can  be  used  and  connected 
as  shown  in  fig.  32.  For  large  stations,  either  a  very 
large  double  or  triple  pole  double  throw  switch  can  be 
used.  The  aerial  switch  is  conveniently  located,  prefer- 


Auxiliary  Apparatus. 


99 


ably  at  the  point  where  the  aerial  leads  enter  the  oper- 
ating room.  A  switch  which  allows  of  rapid  change  from 
sending  to  receiving  instruments  and  vice  versa  is  a  de- 
sideratum, one  type  of  such  a  key  being  shown  in  fig.  33. 
The  details  of  construction  are  left  to  the  reader,  the 
essentials  being  that  the  contacts  and  switch  pieces  should 
be  well  insulated  from  each  other,  it  being  desirable  to 
use  hard  rubber  throughout.  On  account  of  the  leverage 
it  is  only  necessary  to  move  the  handle  a  short  distance 


Stn<T»n^ 
Ua1V««i«iits 


P.E. 


from  the  sending  to  the  receiving  position.     The  blades 
correspond  to  the  radii  of  a  circle  in  this  type. 

AUTOMATIC  AERIAL  SWITCH. 

This  form  is  very  much  desired  and  used  by  experi- 
menters. It  automatically  disconnects  the  receiving  set 
the  instant  that  the  key  is  used  to  send  and  as  soon  as  the 
message  is  sent,  the  receiving  set  is  again  ready  to  receive. 
This  particular  embodiment  is  adapted  to  a  closed  circuit 
transmitter.  The  figure  (34)  is  self  explanatory,  and 
the  reader  will  have  little  difficulty  in  making  and  attach- 
ing this  arrangement  to  an  ordinary  key.  Credit  for  the 
design  is  due  to  Mr.  G.  S.  Vernam.*  German  silver  or 

*C.  W.  Bui. 


100 


Experimental  Wireless  Stations. 


brass  may  be  used  for  the  springs  and  platinum  is  desir- 


Contacts 


HE,  33 


able  for  the  contacts.     The  spring  strips  are  insulated  by 


Auxiliary  Apparatus.  : 


ioi 


hard  rubber  or  fibre  bushings  and  rubber  tubing,  the  whole 
being  clamped  together  by  two  brass  machine  screws.  A 
short  brass  strip  is  used  to  attach  the  device  firmly  to  the 
back  end  of  the  key  lever.  The  springs  must  be  adjusted 
so  that  the  first  two  and  the  second  two  make  contact 


FIE.  3  4. 


Apparatus 


when  the  key  is  up,  and  the  second  makes  contact  with 
the  fourth  when  the  key  is  down.  This  will  be  clear  by 
referring  to  the  diagram.  Connections  may  be  soldered 
to  the  lugs  on  the  springs. 

AUTOMATIC  SWITCH  FOR  HEAVY  CURRENTS. 

The  foregoing  switch  is  only  suited  to  small  stations. 
The  one  shown  in  fig.  35  is  adapted  for  heavy  currents 
and  is  also  suitable  for  an  inductively  coupled  transmitter. 
The  key  is  not  materially  different  from  the  foregoing 
and  can  be  readily  understood  and  constructed  from  the 
diagram.  The  object  of  these  keys  is  to  protect  the  re- 


402 


Wireless  Stations. 


ceiving  detector  from  injury  while  sending  and  they  oper- 
ate through  the  sending  inductance.  This  increases  the 
wave  length  of  the  aerial  for  receiving  to  some  extent, 
but  is  not  harmful.  This  particular  form  is  suited  for 
both  close  and  inductively  coupled  transmitters  or  re- 
ceivers. As  in  the  other  arrangement,  the  hard  rubber 
sheet  is  arranged  on  the  key,  being  placed  between  the 
button  and  the  key  lever  in  this  case.  Credit  for  this 
arrangement  is  due  to  Mr.  N.  M.  Tate.*  It  is  also  sat- 


O    n    o 


FIG, 35 


is  factory  to  mount  the  contacts  on  the  back  of  the  key 
on  the  adjustment  screw. 

IN  GENERAL. 

The  wiring  in  a  wireless  station  should  be  carried  out 
in  accordance  with  the  code  requirements.  A  copy  of 
the  requirements  may  be  had  gratis  by  addressing  the 
National  Board  of  Fire  Underwriters  at  either  New 
York,  Chicago  or  Boston. 

*  Mod.  Electrics. 


CHAPTER  VIII. 


TRANSMITTING  CONDENSERS. 

A  condenser  is  a  device  which  stores  energy  and  in 
its  simplest  form  it  consists  of  two  coatings  of  tin  foil 
separated  by  an  insulating  substance,  such  as  air,  paper, 
glass,  or  oil,  which  is  called  a  dielectric.  The  two  coat- 
ings are  insulated  from  each  other  as  far  as  metallic  con- 
nections are  concerned  and  if  they  are  charged  by  means 
of  an  induction  coil  or  transformer  they  will  discharge 
with  a  brilliant  crackling  spark  when  connected  through  a 
suitable  gap.  Now  this  discharge  occurs  so  rapidly  that 
it  appears  to  be  a  single  discharge,  but  it  is  in  fact  made 
up  of  a  number  of  rapidly  oscillating  discharges,  first  in 
one  direction  and  then  in  another.  During  this  process 
the  polarity  of  the  charge  on  the  two  coatings  is  rapidly 
reversed  so  that  a  given  coating  is  first  charged  in  one 
polarity  and  then  in  another  at  a  high  rate.  The  vibra- 
tions from  the  discharge  are  called  oscillations  and  grad- 
ually die  out  with  more  or  less  rapidity  according  to  the 
degree  of  damping.  The  reason  why  a  spark  gap  causes 
damping  will  be  discussed  when  the  matter  of  spark  gaps 
is  taken  up.  The  time  taken  by  an  ordinary  discharge  is 
generally  a  small  part  of  a  second,  but  during  this  small 
space  of  time  there  may  be  as  many  as  100,000  to 
1,000,000  oscillations. 

Now  the  nature  and  amount  of  this  charge  depends 
on  the  dielectric  rather  than  the  coatings  employed.  It 
has  been  definitely  established  that  the  charge  of  a  con- 


104  Experimental  Wireless  Stations. 

denser  resides  on  the  respective  surfaces  of  the  dielectric 
and  not  on  the  coatings  or  tin  foil.  When  a  condenser  is 
charged  and  the  coatings  removed,  tests  will  show  that 
they  are  not  electrified  to  any  appreciable  extent,  but  if 
they  are  returned  to  position  to  form  a  complete  con- 
denser with  the  same  dielectric,  they  will  form  a  highly 
charged  condenser  again.  The  dielectric  of  a  condenser 
actually  undergoes  a  strain  and  as  in  the  case  of  mechan- 
ical strains,  this  results  in  heat  after  a  time. 

The  two  coatings  of  a  condenser  are  always  charged 
oppositely,  that  is  when  one  coat  is  charged  positively, 
the  other  is  charged  negatively.  These  charges  in  oscil- 
lating back  and  forth  travel  at  a  speed  of  300,000,000 
meters  per  second  or  the  speed  of  light.  When  a  con- 
denser is  charged  by  a  transformer,  there  are  four  stages 
as  follows : 

1.  First  quarter  cycle,  condenser  coatings  are  charged 
to  the  potential  of  the  impressed  E.  M.  F. 

2.  E.  M.  F.  decrease  during  the  second  quarter  cycle 
so  the  charges  on  the  coatings  rush  back  to  the  trans- 
former.    (A  discharge  occurs  in  the  spark  gap  at  this 
point,  resulting  in  oscillations  as  has  just  been  described.) 

3.  Third  quarter  cycle.     Same  as  the  first  quarter 
cycle  except  that  the  direction  and  polarity  of  the  charge 
is  reversed. 

4.  Fourth  quarter  cycle ;  same  as  second  quarter,     A 
second  discharge  occurs  in  the  gap. 

There  are  two  discharges  at  the  least  for  each  cycle, 
or  if  the  frequency  of  the  transformer  is  60  cycles  there 
will  be  at  least  120  discharges  per  second.*  The  higher 


*  A  large  number  of  discharges  is  obtained  by  inter- 
rupting the  natural  discharges  with  a  rotary  gap.  See 
Chapter  10. 


Transmitting  Condensers.  105 

the  frequency  of  the  impressed  E.  M.  F.  is,  the  higher  will 
be  the  value  of  the  circuit  including  the  capacity,  because 
of  the  increased  rate  of  change  of  flux.  An  increase  of 
the  capacity  within  limits  also  aids  in  increasing  the  cur- 
rent. In  wireless  work,  a  capacity  or  condenser  behaves 
in  the  following  definite  manner : 

1.  The  apparent  conductivity  is  directly  proportional 
to  the  capacity  and  the  frequency  of  the  E.  M.  F. 

2.  The  apparent  resistance  or  capacity  reactance  is 
inversely  proportional  to  the  capacity  and  the  frequency 
of  the  E.  M.  F. 

We  have  already  seen  how  the  capacity  required  for  a 
given  transformer  may  be  found.  All  that  remains  then 
is  to  find  the  dimensions  for  a  condenser  which  will  give 
the  required  capacity. 

CALCULATION  OF  CAPACITY. 

Now,  in  order  to  standardize  experimental  apparatus, 
the  author  considers  that  the  parallel  plate  type  of  con- 
denser is  the  best  to  adopt  because  its  capacity  or  a  desired 
capacity  can  be  readily  calculated.  The  formula  is, 

C  =    k  A 

c.  g.  s.  electrostatic  units. 

4/£  d 

in  which,  C  represents  the  capacity,  k,  the  dielectric  con- 
stant, air  or  other  gas  at  atmospheric  pressure  being  prac- 
tically 1.  Other  values  of  k  for  different  dielectrics  will 
be  found  in  the  Table  of  Dielectrics.  A  represents  the 
area  of  one  of  the  plates  overlapped  by  the  other  plate, 
and  d  is  the  distance  apart  of  the  plates  in  centimeters. 
This  formula  is  accurate  only  when  the  distance  between 
the  two  plates  is  relatively  small  in  comparison  with  the 
length  and  breadth  of  the  plates. 


106  Experimental  Wireless  Stations. 

This  may  be  expressed. 

C=_KA___  or  C4  n  D  x  9  x  105  =  KA 

4  n  Dx9xlQ6 
to  express  the  capacity  in  microfarads. 

To  find  the  desired  area,  this  may  be  arranged, 
A  =  36.  TrPCxIQ5 
K 

DIELECTRIC  TABLE. 
(K)    Constants  for, 

Air,  empty  space,  or  gases  at  atmospheric  pres- 
sure    1. 

Glass 6.      to    10 

Light  flint  glass 6.5 

Dense  flint  glass 6.5    to    10 

Hard  crown  glass 7. 

Mica  6.6    to  7.5 

Hard  rubber 2.7 

Kerosene  oil 2. 

Castor  oil 4.78 

Shellac 2.7    to  3.5 

Ebonite  2.5    to  3. 

Manilla  paper 1.5 

Paraffin 1.75  to  2.3 

Resin 1.77  to  2.5 

Porcelain 4.38 

Water  80. 

Note,  an  average  result  is  best  to  use  in  the  formula. 
Glass  should  be  taken  as  7j^  or  8  when  ordinary  glass  or 
old  photographic  plates  are  to  be  used.  The  emulsion 
should  be  cleaned  off  before  using  the  latter. 


Transmitting  Condensers.  107 

Now  the  quantity  36  pi  x  100,000  is  the  same  in  every 
case,  so  the  formula  may  be  simplified  to 

A  =  DC  x  11309760,  and  when  glass  is  used  for  the 
K 

dielectric,  which  has  a  constant  of  8 ;  this  may  be  further 
simplified  to 

A  =  DC  x  1413720     because  1 1309760  =  1413720. 


8 

So  the  calculation  of  the  capacity  and  area  for  a  given 
or  desired  condenser  is  really  not  difficult.  The  figures 
are  in  the  metric  system  and  to  change  to  inches  after  the 
area  has  been  found  in  centimeters  change  in  the  follow- 
ing ratio : 

1  inch  =  2.54  centimeters.     1  centimeter  =  .3937  in. 
1  square  inch  =  6.45  sq.  cm.      1  sq.  cm.  =  .1550  sq.  in. 

In  order  to  illustrate  the  use  of  this  formula, — suppose 
it  is  desired  to  find  the  necessary  area  for  the  tinfoil  to 
make  up  a  condenser  of  .002  microfarad,  using  glass  .1 
centimeter  thick.  Ordinary  glass  plates  are  .05  inch  thick 
or  approximately  .125  centimeter  thick.  Using  the  sim- 
plified formula,  we  get 

A  =  .1  x  .002  x  1413720  =  282.74  sq.  cm. 

Now  this  surface  can  be  apportioned  in  almost  any 
desired  manner.  For  instance,  three  plates  of  glass  of 
this  size  12  by  14  centimeters  and  covered  with  tin  foil  on 
each  side,  9  by  10j^  centimeters  would  be  approximately 
right. 

To  take  another  example, — desired  capacity  .02  micro- 
farad, using  manilla  paper  .02  cm.  thick, — what  area  of 
foil  for  A  is  required. 


108  Experimental  Wireless  Stations. 

Use  the  simplified  general  formula, 
A  =  DC  x  11309760,  substituting 

K 

A  =  .02  x  .02  x  11309760  =  4523.9  =  3015.9  sq.  cm. 
1.5  1.5 

This  can  also  be  proportioned  as  desired,  about  30 
sheets  of  the  dielectric  being  used. 

Almost  any  desired  capacity  can  be  worked  out  to  a 
close  degree  of  accuracy  in  this  manner.  These  quanti- 
ties have  been  carefully  worked  out.  It  will  be  noted 
from  the  formula  that  there  are  several  factors  which  de- 
termine the  capacity  of  a  condenser,  A,  D,  and  K,  so  that 
if  two  are  known,  the  third  may  be  found. 

Now  in  designing  a  condenser  for  transmission  pur- 
poses, the  thickness  of  the  dielectric  must  be  sufficient  to 
withstand  the  impressed  voltage  and  an  overload  without 
puncturing.  For  this  reason  one  centimeter  to  every  40,- 
000  volts  should  be  allowed.  Thus  if  the  voltage  is  10,000 
the  dielectric  should  be  made  .25  centimeters  thick  and  so 
on.  However,  if  glass  can  not  be  had  in  this  size  or  a 
large  enough  size,  two  or  more  capacities  of  the  same  di- 
mensions can  be  connected  together,  in  series.  This  meth- 
od makes  the  use  of  ordinary  thickness  of  glass  possible 
with  high  voltages,  but  since  the  capacity  is  thereby  cut 
down,  in  approximately  the  same  ratio,  the  capacity  for 
each  unit  must  be  correspondingly  larger.  Thus  if  a  sin- 
gle unit  is  used  which  has  a  capacity  of  .2  microfarad,  and 
if  two  condensers  must  be  used  in  series  to  secure  this 
same  capacity  without  breaking  down  under  the  impressed 
voltage,  each  must  have  a  capacity  of  .4  microfarad.  So 
that  to  increase  the  voltage  which  a  condenser  made  up  of 
a  given  size  of  plates  may  stand,  by  connecting  units  in 


Transmitting  Condensers.  109 

series,  to  twice  the  voltage  which  a  single  unit  can  stand, 
each  unit  must  have  twice  the  capacity  of  a  single  unit  if 
two  are  connected  in  series  to  give  the  capacity  of  the  sin- 
gle unit.  While  we  are  on  this  subject,  it  is  well  to  note 
that  when  condenser  units  are  connected  in  parallel,  the 
total  capacity  is  the  sum  of  the  capacities  of  the  condenser 
units,  but  the  puncturing  voltage  which  the  parallel  set 
can  stand  is  limited  to  that  of  its  weakest  unit.  For  this 
reason  the  units  used  should  be  of  identical  dimensions 
whenever  possible. 

STRUCTURAL  CONSIDERATIONS. 

The  condenser  is  a  very  important  part  of  the  wireless 
station  and  unless  properly  constructed,  the  transmission 
efficiency  will  be  materially  affected.  The  main  require- 
ments are, 

1.  The  foil  used  should  be  a  good  conductor  and  of 
sufficient  size  to  carry  the  charges  without  undue  heating. 
Copper  is  preferably  used  and  may  be  had  in  thin  sheets 
for  this  purpose.    Tin  foil  should  be  heavy  if  used  at  all. 
The  kind  used  by  florists  is  generally  suitable.    The  high 
frequency  currents  require  a  large  surface  and  if  this  is 
not  provided,  the  conductor  is  likely  to  burn  up. 

2.  Radiation  surface  is  necessary  to  dissipate  the  heat 
which  is  generated  in  the  dielectric.    When  used  in  air, 
the  condenser  plates  are  generally  spaced  a  short  distance 
apart  for  this  purpose,  and  when  immersed  in  oil,  the 
liquid  acts  as  a  cooling  agent. 

3.  Contacts  should  be  soldered  to  the  tin  or  copper 
sheets  forming  the  coatings  to  make  the  best  contact  pos- 
sible.    The  resistance  of  poor  joints  to  high  frequency 
currents  is  much  greater  than  to  low  frequency  currents. 
Stranded  conductors  make  good  leads  to  condensers.    A 


110  Experimental  Wireless  Stations. 

common  method  of  construction  is  to  clamp  projecting 
portions  of  the  coatings  tightly  together  to  form  a  single 
conductor  at  the  terminals. 

4.  Brush  discharges,  surface  leakage,  and  other  losses 
should  be  minimized.  This  is  accomplished  by  using  a 
good  grade  of  dielectric,  allowing  a  safe  margin  around 
the  coatings,  making  the  coatings  uniform  and  even,  mak- 
ing the  coatings  fit  the  dielectric  tightly,  and  placing  the 
complete  condenser  in  an  insulator  such  as  boiled  linseed 
oil. 

(5)  Contacts  should  be  as  large  as  possible,  to  avoid 
undue  resistance. 

The  items  under  (4)  are  perhaps  the  most  important 
and  require  careful  attention  in  designing  and  construct- 
ing a  condenser.  Plate  condensers  offer  the  most  satis- 
factory solution  to  the  several  problems  and  in  addition 
have  the  advantage  already  mentioned  of  being  readily 
calculated  for  a  given  purpose.  Plate  condensers  sep- 
arated in  air  are  not  as  desirable  as  those  imbedded  in  an 
insulator  because  they  tend  to  blister  and  aid  brush  dis- 
charges under  overloads.  For  these  reasons,  the  standard 
type  to  be  adopted,  is  the  plate  condenser  made  into  con- 
venient or  desired  units  and  imbedded  in  an  insulator. 

DETAILS. 

The  glass  used  may  be  had  cut  to  size  at  any  hardware 
or  paint  supply  house  and  for  voltages  over  15,000  the 
use  of  double  strength  glass  is  advisable.  Data  regard- 
ing the  sizes,  thickness  and  so  on  may  be  had  from  the 
dealer  and  is  useful  in  calculating  capacity,  estimating 
material,  and  similar  purposes.  Old  photographic  plates 
make  very  good  condenser  dielectric  material  when  the 
emulsion  is  removed  and  may  be  had  very  cheap.  The 


Transmitting  Condensers.  Ill 

author  once  purchased  two  hundred  5x7  glass  plates  at 
25c  per  hundred,  and  while  the  larger  sizes  are  valued 
higher  because  of  their  use  in  picture  frames,  they  may 
be  had  for  a  nominal  sum.  In  fact,  many  photographers 
will  gladly  donate  old  glass  plates  if  properly  approached 
and  told  that  they  are  for  wireless  experimental  purposes. 
The  emulsion  can  be  removed  by  soaking  the  plates  over- 
night in  a  strong  solution  of  lye  in  water.  Glass  contain- 
ing much  lead  is  not  suited  for  condensers,  and  all  of  the 
plates  used  should  be  of  the  same  thickness  throughout. 

Just  before  using,  it  is  advisable  to  again  clean  the 
plates  with  a  rag  dipped  into  alcohol,  although  warm 
water  can  be  used  if  the  plates  are  allowed  to  thoroughly 
dry  afterwards.  The  glass  should  be  thoroughly  clean 
and  dry  before  using. 

MATERIAL  FOR  COATINGS. 

Thin  copper  sheet  or  heavy  tin  foil  should  be  used  for 
the  coatings  and  should  be  cut  to  size.  If  tin  foil  is  used, 
it  should  be  about  No.  35  gauge  if  possible,  and  in  any 
case  it  must  be  smoothed,  by  means  of  a  print  roller  such 
as  photographers  use.  In  making  condensers  which  are 
so  large  that  a  single  width  of  tin  foil  will  not  suffice,  two 
or  three  strips  overlapping  each  other  can  be  used.  The 
size  of  the  coatings  should  be  such  that  a  margin  of  one 
inch  is  left  on  all  sides  relative  to  the  edge  of  the  glass 
plate  for  every  ten  thousand  volts  to  be  used  in  the  charg- 
ing, though  less  may  be  used  after  a  limit  of  two  or  three 
inches  is  reached,  or  when  the  plates  are  immersed  in  oil. 

ARRANGEMENT. 

The  arrangement  of  the  plates  and  coatings  is  shown 
in  fig.  36.  The  lugs  for  the  coatings  are  preferably  in 
one  piece  with  the  coatings,  but  they  may  be  separate 


112 


Experimental  Wireless  Stations. 


pieces  if  they  make  good  contact  electrically  with  the 
coatings  and  are  mechanically  strong.  The  latter  method 
is  less  expensive  as  there  is  practically  no  waste  of  ma- 
terial. 

In  soldering  tinfoil,  the  foil  to  which  a  strip  is  to  be 
soldered  must  be  laid  upon  a  piece  of  copper  or  aluminum 
sheet  of  some  thickness,  in  order  to  conduct  the  heat 


away,  as  the  foil  will  melt  or  burn  up,  otherwise.  When 
the  condenser  is  to  be  used  on  high  voltage,  two  or  three 
thicknesses  of  the  glass  can  be  used  between  each  sheet  of 
foil  to  secure  a  greater  disruptive  strength,  but  the  capa- 
city is  of  course  correspondingly  less  and  the  total  thick- 
ness of  the  plates  between  the  two  coatings  must  be  used 
to  calculate  the  capacity. 

The  alternate  lugs  of  the  two  coatings  can  be  brought 


Transmitting  Condensers.  113 

out  on  opposite  sides  of  the  plates  or  else  suitably  spaced 
on  the  same  side.  (See  the  figure.)  It  is  a  good  plan 
to  make  the  required  condenser  in  several  units,  particu- 
larly if  the  capacity  is  large.  Thus  if  twelve  8x10  plates 
are  to  be  used,  two  units  each  having  six  plates  are  prefer- 
able. This  arrangement  makes  repairs  from  damages  or 
punctures  easier,  since  only  one  of  the  units  is  liable  to 
be  punctured  at  a  time,  while  with  a  single  unit,  the  whole 
condenser  would  be  temporarily  disabled.  It  is  good 
practice  to  provide  an  extra  unit  or  two  if  this  method  is 
adopted,  in  order  to  meet  emergencies. 

In  building  the  condenser,  lay  a  sheet  of  glass  on  a 
flat  table,  then  place  a  sheet  of  foil  with  its  lug  on  top 
of  it,  so  that  it  lies  flat  and  is  evenly  spaced  from  the  edge 
of  the  plate.  Now  lay  a  second  glass  plate  on  top  of  this, 
and  place  a  second  sheet  of  foil  on  it,  spaced  as  before,  but 
arranged  so  that  its  lug  comes  either  at  the  opposite  side 
of  the  plate  or  suitably  spaced  from  the  first  lug,  as  shown 
in  the  figure.  Proceed  as  before,  placing  alternate  sheets 
of  glass  and  foil  until  all  of  the  plates  have  been  assem- 
bled. An  extra  plate  should  then  be  used  to  cover  the  top 
sheet  of  foil.  When  this  is  done,  the  condenser  will  be 
a  uniform  unit,  with  two  sets  of  insulated  plates  alternate- 
ly arranged.  The  unit  can  then  be  bound  together  by  large 
rubber  bands,  rubber  tape  or  string,  or  any  suitable  form 
of  clamp  may  be  used  provided  too  much  pressure  is  not 
applied.  If  the  plates  are  pressed  together  too  tightly 
the  glass  will  crack,  ruining  the  condenser.  The  two 
respective  sets  of  lugs  should  now  be  firmly  clamped  be- 
tween brass  or  copper  sheet,  or  soldered  together  and  to 
a  large  lead.  Test  the  unit  for  short  circuits  with  a  bat- 
tery and  telephone  receiver,  (the  faint  response  does  not 
indicate  a  short  circuit,  but  is  caused  by  the  capacity  of 
the  plates).  A  few  of  the  lugs  can  be  left  disconnected 


114  Experimental  Wireless  Stations. 

as  shown  at  (c)  fig.  36,  and  separate  leads  attached  to 
them  so  that  the  capacity  of  the  condenser  can  be  varied 
a  little.  This  method  is  useful  particularly  with  spark  coils 
since  the  exact  capacity  needed  is  difficult  to  predetermine. 

The  finished  units  should  be  placed  in  a  suitable  box  or 
jar,  (hard  rubber  or  glass  storage  battery  jars  are  excel- 
lent containers  for  this  purpose),  a  hard  rubber  cover 
provided,  connections  brought  to  binding  posts,  and  so  on 
as  desired.  The  jar  or  container  should  be  liquid  proof 
and  should  be  filled  with  a  good  quality  of  transformer 
oil,  boiled  linseed  oil,  castor  oil,  vaseline,  paraffme  oil,  or 
other  non-explosive  insulating  oil.  The  condenser  should 
be  mounted  or  arranged  in  the  jar  so  that  it  does  not  rattle 
and  if  the  condenser  is  to  be  moved  very  much  a  thick  in- 
sulator like  vaseline  should  be  used,  so  that  the  oil  will 
not  be  continually  running  over  or  leaking.  A  good  grade 
of  lubricating  oil  can  be  used,  the  non-carbonizing  oils 
used  in  automobiles  being  suitable  and  quite  cheap.  Oils 
which  ignite  easily  or  which  carbonize  or  deteriorate 
quickly,  as  well  as  those  which  are  poor  insulators  should 
not  be  used,  since  the  function  of  the  oil  is  to  prevent 
leakage  and  brush  discharges  as  well  as  to  dissipate  the 
heat  caused  by  the  hysteresis  of  the  glass  dielectric. 

A  condenser  is  really  a  very  simple  piece  of  apparatus, 
but  too  much  care  cannot  be  taken  in  constructing  it  if 
efficiency  is  desired.  For  experimental  purposes,  old 
bottles,  placed  in  a  dishpan  containing  salt  water,  and 
filled  two-thirds  full  with  a  solution  of  common  salt  and 
water  can  be  impressed  into  service  as  a  condenser,  con- 
nections being  made  to  the  dishpan  and  to  wires  entering 
into  the  bottles  respectively.  A  large  capacity  is  possible 
by  this  makeshift  arrangement,  but  the  capacity  can  of 
course  not  be  accurately  determined.  Two  rubber  cov- 
ered wires  twisted  together  but  insulated  at  the  ends  will 


Transmitting  Condensers.  115 

form  a  condenser  when  connected  about  the  secondary 
terminals  of  a  small  coil.     There  are  many  similar  ar- 
rangements which  will  suggest  themselves  to  the  reader. 
There  are  other  suitable  forms  for  condensers,  but  since 
the  type  described  is  equal  or  superior  to  them  and  serves 
for  all  experimental  purposes,  these  will  not  be  described. 
By  using  copper,  zinc,  or  even  tin  sheets  (iron  coated 
with  tin),  of  some  thickness  between  glass  plates,  a  vari- 
able condenser  may  be  made.     The  capacity  can  be  varied 
by  moving  the  plates  forming  one  set  of  coatings  in  or  out 
of  the  vicinity  of  the  glass  plates  and  the  other  set  of 
coatings,  thus  increasing  or  diminishing  the  capacity.    The 
construction  of  such  an  arrangement  is  very  simple  and 
the  details  need  no  further  comment.     The  diagram  of 
this  arrangement  is  shown  in  fig.  36  (d).     It  should  be 
noted  that  this  arrangement  is  just  like  an  ordinary  glass 
plate  condenser  except  that  rigid  movable  plates  are  sub- 
stituted for  the  tinfoil  in  one  of  the  sets  of  coatings.     In 
fig.  36,  (e)  shows  the  manner  of  connecting  condensers  in 
parallel  to  increase  the  capacity,  (f)  shows  the  connec- 
tions for  series  to  decrease  the  capacity,  and  (g)  shows 
a  combination  of  the  two,  which  decreases  the  capacity. 
Taking  a  single  unit  for  comparison,  the  units  being  of 
the  same  size  (e)  will  give  double  the  capacity,  (f)  one- 
half  the  capacity,  and  (g)  an  equal  capacity,  but  using 
four  units.    The  series  and  series  multiple  connections  are 
used  when  the  voltage  impressed  on  a  single  unit  is  more 
than  it  can  stand  without  puncturing,     (h)  fig.  36  shows 
the  method  used  to  connect  both  a  fixed  and  a  variable 
condenser  having  the  same  form  and  size  of  dielectric  in 
circuit.     This  method  allows  the  exact  capacity  needed 
for  a  given  transformer  to  be  used.     With  this  arrange- 
ment, the  variable  condenser  need  not  have  a  very  large 
capacity  by  itself  since  it  is  needed  only  to  make  up  a 
small  difference  in  most  cases. 


CHAPTER  IX. 


CALCULATION  OF  INDUCTANCE.    CONSTRUC- 
TION OF  HELIX  AND  OSCILLATION 
TRANSFORMER. 

Like  the  calculation  of  wave  length  and  capacity,  the 
calculation  of  inductance  is  quite  simple  provided  the  fol- 
lowing formulas  are  used.  The  answer  is  of  course  only 
approximately  correct,  but  this  is  quite  accurate  and  may 
be  used  directly  in  supplying  the  proper  inductance  in  the 
transmitting  circuit.  The  calculation  for  self  inductance 
takes  into  account  the  magnetic  circuit  of  the  coil  and  the 
number  of  turns  of  wire  in  the  coil.  Any  change  in  the 
shape  or  size  of  a  coil  will  alter  the  inductance  and  spe- 
cial shapes  require  special  formulas.  The  following  rela- 
tion holds  good,  however,  for  cylindrical  coils  of  one 
layer,  as  helixes  or  choke  coils,  and  takes  into  account 
variable  factors. 

(1)      (SxDxT)2  =  inductance  in  centimeters. 

M+  1/3D 

In  this  formula, 

D  is  the  diameter  of  the  coil  in  inches. 
T  is  the  total  number  of  turns  of  wire. 
M  is  the  length  of  the  coil  in  inches. 


Inductance  for  Transmitters.  117 

The  result  is  expressed  in  centimeters,  which  may  be 
changed  into  microhenrys  by  dividing  the  result  by  1,000. 

To  illustrate  the  use  of  this  formula,  find  the  induct- 
ance of  a  coil  nine  inches  in  diameter,  10  inches  long  and 
having  10  turns  of  wire. 

(  5  x 9  x  10  )2      =  4502  =202,500 

10+1/3  of  9          ~~13~     "13" 
or  15,580  cm.  approximately,  or  15.580  microhenrys. 

Another  formula  which  may  be  used  to  find  the  in- 
ductance of  a  helix  in  C.  G.  S.  units  is, 

(2)     Inductance  (L)  =  1    (3.1416  dn),2  where 

1,  is  the  length  of  the  helix,  d  its  diameter,  and  n  the 
number  of  turns  per  unit  length.  Thus  with  this  form- 
ula, a  helix  5  cm.  in  diameter,  50  cm.  long  and  having  2 
turns  to  each  cm.,  has  an  inductance  of 

50  (3.1416 .  5.2) 2  =  50,000  C.  G.  S. 

1  henry  is  equal  to  1,000,000,000  C.  G.  S.  electromag- 
netic units. 

To  calculate  the  inductance  of  flat  or  doughnut  helixes 
or  coils  (those  having  several  layers  wound  over  each 
other),  the  formula  to  use  is, 

(3) 

(5XDXT)2 

1/3D  +  3/2M  +  5/4N      =  inductance  in  cms., 
in  which 

D  is  the  average  diameter  of  the  coil  in  inches. 

M  is  the  length  of  the  coil  in  inches. 

N  is  the  depth  of  the  coil  in  inches. 

T  is  the  total  number  of  turns  of  the  coil. 

To  illustrate :  Given  a  flat  type  of  helix  of  the  fol- 
lowing dimensions,  calculate  the  inductance,  6  turns  of 
copper  strip  1  in.  apart,  depth  of  winding  6  in.  Width  of 


118  Experimental  Wireless  Stations. 

strip  is  1  in.  and  average  diameter  12  inches.     (Inside  6 
in.,  outside  18  in.) 

(  5  x  12  x  6  )2  =  (360)2  =  129,600  or  9970  cm. 
4+l^  +  7>£       ~13~~          13 

or  9.970  microhenrys. 

MUTUAL  INDUCTANCE. 

In  oscillation  transformers,  mutual  induction  must  be 
considered.  When  the  transformer  is  a  long  single  layer 
coil  having  a  lumped  secondary  wound  about  it,  the  form- 
ula is, 

(4)     M  =  4  X  3.1416  nNA    C.  G.  S.  units. 

M  is  the  mutual  inductance,  n  the  number  of  turns  per 
cm.  on  the  primary  coil,  N  the  total  number  of  turns  on 
the  secondary  coil,  and  A  represents  the  area  of  cross 
section  included  within  the  primary  coil.  The  length  is 
to  be  measured  in  centimeters. 

1  henry  is  equal  to  1,000,000,000  C.  G.  S.  electromag- 
netic units. 

1  microhenry  is  one  millionth  of  a  henry. 

STANDARD  HELIX. 

For  small  stations  the  helix  is  perhaps  better  suited 
than  the  oscillation  transformer  and  since  it  is  easier  to 
calculate  and  construct,  it  will  be  described  first.  The  ar- 
rangement and  details  of  the  helix  are  shown  in  fig.  37. 
The  heads  may  be  cut  out  of  hardwood  on  a  bandsaw  or 
else  turned  out  in  a  lathe,  and  should  be  eight  inches  in 
diameter  and  preferably  £4  of  an  inch  thick.  These  heads 
are  separated  at  a  distance  of  7  inches  by  four  evenly 
spaced  pieces,  each  24  of  an  inch  thick  by  1  inch  wide  by 


Inductance  for  Transmitters. 


119 


inches  long.  These  pieces  should  be  smoothly  fin- 
ished. While  the  wire  will  stay  on  these  pieces  without 
artificial  support,  it  is  advisable  to  cut  notches  in  these 
pieces  to  receive  the  wire.  If  possible,  the  outer  surface 
of  the  pieces  should  be  veneered  with  strips  of  hard 
rubber  or  fibre  as  extra  insulation  so  that  the  wire  does 
not  make  direct  contact  with  the  wood.  The  separating 
strips  are  arranged  as  shown  so  that  they  form  legs  J4 


P.E. 


of  an  inch  high  at  the  bottom.  The  construction  is  quite 
simple,  and  if  possible  insulators  should  be  substituted  for 
the  wood  legs,  in  which  case,  the  upright  pieces  will  be 
made  £4  of  an  inch  shorter.  The  frame  may  be  fastened 
together  by  screws  and  glue  and  should  set  true.  The 
wire  used  is  No  4  B&S  brass,  aluminum  or  copper,  and 
should  be  purchased  already  coiled  to  approximately  9 
inches  in  diameter  or  a  little  less.  When  wound,  the 


120  Experimental  Wireless  Stations. 


wire  will  have  a  diameter  of  10  inches  and  will  stay  tight 
if  of  smaller  diameter  to  begin  with.  The  wire  is  wound 
on  the  notches,  so  that  the  turns  are  spaced  J4  of  an  inch 
apart  in  a  uniform  and  even  winding.  Seven  complete 
turns  are  required  so  that  about  \9l/2  feet  of  wire  are 
necessary.  This  wire  can  be  had  at  supply  houses  or 
hardware  stores.  The  wire  turns  will  start  and  end  just 
a  little  less  than  one  inch  from  each  head,  and  the  ends 
can  be  fastened  down  by  large  screw  binding  posts.  The 
turns  should  be  kept  £4  of  an  inch  apart  and  10  inches 
in  diameter  for  the  purpose  of  standardization.  This 
arrangement  will  be  most  suited  for  the  low  wave  length 
and  will  give  fairly  sharp  tuning.  If  the  turns  are  made 
larger  in  diameter,  the  tuning  will  be  less  definite,  and  if 
more  turns  are  used  the  wave  length  is  of  course  in- 
creased. However,  if  the  inductance  is  made  too  large 
for  the  aerial,  the  period  and  the  radiation  are  cut  down. 
Small  aerials  must  naturally  have  relatively  small  helixes 
to  maintain  the  necessary  balance.  Flexible  contacts  or 
helix  clips  should  be  provided,  as  shown.  Almost  any 
desired  size  of  inductance  may  be  constructed  along  these 
same  lines,  and  this  standard  is  highly  recommended  for 
stations  up  to  1  K.  W.  using  the  low  standard  wave 
length. 

This  helix  has  a  maximum  inductance  of  approxi- 
mately 14.28  microhenrys.  One  complete  turn  has  an  in- 
ductance of  .291  microhenry.  To  find  the  inductance  for 
any  number  of  turns,  multiply  <291  by  the  square  of  the 
number  of  turns.  Thus  for  three  turns,  multiply  .291 
by  9,  for  Zy2  turns,  by  12 J4,  and  so  on. 

In  practice,  from  one  to  three  turns  will  be  needed 
in  the  condenser  circuit,  according  to  the  capacity  of 
the  condenser  used,  and  while  all  of  the  seven  turns 
may  never  be  needed,  the  aerial  circuit  will  generally 


Inductance  for  Transmitters.  121 

include  at  least  four  or  five  turns,  depending  upon  its 
dimensions. 

Copper  or  brass  ribbon  or  coiled  strip  is  also  suitable 
for  helix  construction. 

STANDARD  OSCILLATION  TRANSFORMER. 

The  type  to  be  adopted  is  the  flat  pancake  form.  The 
mutual  inductance  is  readily  adjustable  with  this  type, 
and  every  part  of  the  inductances,  can  be  readily  reached. 
This  transformer  allows  of  very  sharp  and  accurate  tun- 
ing and  is  recommended  for  all  stations  using  over  100 
watts  of  energy.  It  will  also  be  useful  to  smaller  sta- 
tions. Brass  ribbon  J^  inch  wide  is  used  in  constructing 
both  the  primary  and  secondary  and  should  be  about  1-16 
of  an  inch  thick.  This  may  be  had  at  hardware  stores. 
About  40  or  42  feet  will  be  needed.  Thinner  ribbon  may 
be  used  double  or  triple  to  make  up  the  desired  thickness. 

Obtain  four  strips  of  rubber  or  fibre  ^x>^  by  14^ 
inches  long.  These  should  be  straight  and  smooth.  Hard- 
wood may  be  substituted.  These  should  be  joined  as 
shown  in  fig.  38,  with  half  joints  at  the  center  to  form 
two  sets  of  crossed  pieces.  Before  gluing  the  joints  the 
pieces  should  be  taken  apart,  marked  and  cut  as  shown. 
The  slots  are  best  cut  with  a  hacksaw  or  band  saw ;  each 
slot  being  1-16  of  an  inch  wide  and  3-8  of  an  inch  deep. 
The  slots  are  placed  exactly  ^2  in.  apart  and  begin  J4  of 
an  inch  from  the  end.  Mark  numbers  1  to  4  on  the  ends 
of  the  strips  as  shown  in  the  figure  so  that  when  the 
two  pieces  are  put  together  again  the  outside  ends  will 
be  in  order. 

The  slots  are  laid  off  beginning  from  the  outside  so 
that  each  slot  is  one-eighth  of  an  inch  closer  to  the  center 
than  the  one  before,  the  slots  thus  forming  a  spiral  when 
the  pieces  are  placed  together.  Proceed  the  same  for  both 


122 


Experimental  Wireless  Stations. 


sets  of  cross  pieces,  except  that  slots  for  five  turns  are 
provided  for  the  set  which  is  to  support  the  primary 
while  the  other  set  is  slotted  for  nine  turns,  thus  coming 
nearer  the  center.  After  the  slotting  is  done,  fasten  the 
pieces  at  the  joints  and  bore  a  hole  three-eighths  of  an 
inch  in  diameter  through  each  set  exactly  at  the  center. 

Now  fasten  the  two  cross  pieces  down  in  a  convenient 
place  by  means  of  one  or  two  screws  at  the  center  hole 
and  wind  the  ribbon  in  the  slots.  The  ribbon  should 
be  either  pressed  or  driven  into  the  slots  with  a  mallet. 
It  is  a  good  plan  to  begin  at  the  inside  to  do  this,  taking 
care  to  make  the  curve  of  the  spiral  as  uniform  as  poss- 


Cr.ss 


ible.  Both  forms  should  be  wound  in  this  manner,  the 
ends  of  the  ribbon  being  cut  and  smoothed  off.  The 
projecting  ends  should  be  sent  slightly  away  from  the 
adjacent  turn  of  the  ribbon.  The  ribbon  should  fit  snugly 
in  the  slots  so  that  it  will  stay  in  place  indefinitely.  The 
curve  of  the  ribbon  should  not  be  too  sharp  at  the  sup- 
port points,  but  should  form  a  gradual  symmetrical  spiral. 
The  completed  coils  may  be  mounted  in  a  number  of 
ways,  suitable  supports  being  shown  at  (c)  and  (d)  of 
the  figure.  In  the  latter  case,  the  primary  is  movable 
axially  as  well  as  longitudinally  with  respect  to  the  sec- 
ondary, this  radial  effect  being  useful  in  tuning  very 


Inductance  for  Transmitters.  123 

sharply.  The  details  of  mounting  may  be  varied  to  suit 
the  individual  case,  a  threaded  metallic  rod,  three-eighths 
of  an  inch  through  which  the  cross  arms  may  pass  and 
be  fastened  at  an  adjustable  distance  being  suitable.  The 
clip  shown  in  the  figure  is  made  from  an  old  10  or  15 
ampere  switch  contact.  An  electrose  or  hard  rubber  han- 
dle is  screwed  on  its  base  end.  Four  of  these  should  be 
used,  two  each  for  the  two  coils.  Similar  pieces  may  be 
easily  made  for  the  clips  if  an  old  switch  is  not  obtainable, 
almost  any  piece  which  will  make  good  contact  with  the 
ribbon,  being  suitable. 

The  inductance  of  the  primary  may  be  calculated  for 
each  turn,  beginning  with  the  center  by  using  formula 
(3),  taking  first  one  turn,  then  the  first  two,  then  the 
first  three,  as  though  they  were  independent  coils.  Or 
if  the  inductance  of  each  turn  beginning  with  the  outside 
is  desired,  a  similar  method  may  be  employed.  The  in- 
ductance for  the  several  turns  is  not  constant  on  account 
of  the  difference  in  diameter  between  each  turn.  The 
values  for  the  turns,  beginning  with  the  outside  turn,  are 
approximately. 

First  turn,  .868  microhenry. 

Two  turns,  3.96  microhenrys. 

Three  turns,  5.7  microhenrys. 

Four  turns,  10.245  microhenrys. 

Five  turns  (maximum  inductance),  13.5  microhenrys. 

When  the  coils  are  mounted  to  form  a  radial  trans- 
former, the  secondary  should  not  be  turned  out  of  a 
parallel  plane  unless  very  sharp  tuning  is  required,  as 
when  it  is  necessary  to  work  through  considerable  inter- 
ference. The  tuning  is  sharper,  within  limits,  the  greater 
the  distance  between  the  two  coils,  but  for  ordinary  pur- 
poses they  should  not  be  too  far  apart  because  the  in- 


124  Experimental  Wireless  Stations. 

tensity  of  the  transmitted  signal  is  considerably  less  with 
a  very  loose  coupling. 

The  secondary  inductance  may  be  similarly  calculated, 
although  this  is  not  necessary,  since  after  the  primary  or 
condenser  circuit  is  tuned  to  a  desired  wave  length,  the 
antenna  circuit  can  be  brought  into  resonance  with  it  by 
connecting  a  number  of  turns  in  the  aerial  circuit  which 
experiment  shows  to  be  right. 

A  LOADING  COIL. 

A  loading  coil  for  the  purpose  of  securing  a  high 
wave  length  for  experimental  purposes  may  be  construct- 
ed like  a  helix  and  inserted  in  series  with  the  aerial  cir- 
cuit, as  has  already  been  explained.  This  loading  coil 
need  not  have  quite  as  large  wire  as  the  sending  helix, 
although  this  size  is  a  desirable  standard,  in  order  to 
avoid  undue  resistance.  No.  8  is  a  common  size  for  this 
purpose.  The  loading  must  not  be  carried  out  too  far 
with  a  given  aerial,  for  after  the  ohmic  resistance  exceeds 
the  square  root  of  four  times  the  inductance  in  henries, 
divided  by  the  capacity  in  microfarads,  the  oscillations 
cannot  take  place.  Any  resistance  impedes  the  oscilla- 
tions considerably.  If  the  long  wave  lengths  are  desired, 
a  large  aerial  capacity  must  therefore  be  provided  to 
begin  with,  if  efficiency  is  desired.  A  small  aerial,  how- 
ever, may  be  loaded  for  experiments. 

Almost  any  circular  coil  of  wire  can  be  made  to  serve 
as  a  helix  or  loading  coil  as  a  makeshift  arrangement, 
but  the  reader  is  strongly  advised  to  adopt  standardized 
instruments  to  make  definite  wave  lengths,  capacities,  in- 
ductances, and  adjustments  possible.  Sharp,  accurate, 
scientific  tuning  and  work  can  be  attained  in  practically 
no  other  way.  The  best  is  not  much  harder  to  make  than 
the  other  kinds  and  is  certainly  well  worth  the  time 
taken,  as  no  other  kind  is  as  easy  and  instructive  to  use. 


CHAPTER  X. 


DESIGN  AND  CONSTRUCTION  OF  SPARK  GAPS. 
PURPOSE  OF  THE  GAP. 

A  spark  gap  is  inserted  in  the  condenser  circuit  to 
allow  the  condenser  to  be  discharged  through  it  until 
the  oscillations  die  out,  and  also  to  prevent  the  conden- 
ser from  discharging  until  it  is  fully  and  properly  charged. 
A  spark  gap,  then,  should  be  a  good  insulator  while  the 
condenser  is  charging  and  a  good  conductor  while  it  is 
discharging.  Now  the  resistance  of  the  spark  gap  is  one 
of  the  main  factors  which  determine  the  damping  of  the 
oscillations,  and  unless  properly  constructed,  considerable 
energy  is  wasted  as  heat  in  this  part  of  the  condenser 
circuit.  The  use  of  the  proper  amount  of  capacity  in  the 
condenser  aids  materially  in  keeping  the  length  of  the 
gap  within  efficient  limits.  Too  long  a  gap  causes  an 
irregular  stringy  spark  while  too  short  a  gap  for  the  given 
condenser  causes  a  wasteful  arc  to  form  in  the  gap.  The 
gap  should,  therefore,  be  of  adjustable  length,  able  to 
conduct  the  energy  without  undue  heating,  and  to  make 
and  break  as  an  insulator  and  conductor  with  rapidity. 
A  poorly  constructed  or  poorly  adjusted  gap  can  cut  down 
the  efficiency  of  transmission  materially.  Three  types 
of  gaps  are  to  be  described,  a  common  gap  for  small 
stations,  a  series  gap  for  somewhat  larger  stations,  and 
a  rotary  gap.  The  quenched  spark  system  will  be  dis- 
cussed in  a  later  chapter. 


126 


Experimental  Wireless  Stations. 


A  simple  gap  is  shown  in  fig.  39.  The  electrodes 
may  be  mounted  in  almost  any  suitable  manner,  care  be- 
ing taken  to  keep  the  two  parts  well  insulated  from  each 
other  and  from  other  bodies.  Either  a  vertical  or  hori- 
zontal mounting  can  be  used  and  if  desired,  only  one  of 
the  electrodes  need  be  adjustable.  The  construction  is 
quite  simple  and  further  comment  seems  unnecessary. 
The  insulation  used  is  preferably  hard  rubber  throughout, 
though  other  materials  may  be  substituted.  The  parts 
are  preferably  made  of  brass  and  the  electrodes  from 


FIG.  33. 


zinc  or  an  alloy  of  zinc  with  2  per  cent  aluminum.  These 
electrodes  should  be  made  removable,  as  they  pit  after 
a  time,  and  should  be  perfectly  true.  It  is  well  to  pur- 
chase these  parts  or  have  them  made  by  a  machinist, 
if  no  lathe  is  available.  The  electrodes  should  have  plenty 
of  surface,  a  diameter  of  J4  mch  f°r  every  hundred  watts 
being  suitable.  If  this  type  of  gap  is  used  with  large 
power,  metallic  radiating  flanges  should  be  provided  to 
take  care  of  the  heat.  The  handle  should  be  well  insu- 


Spark  Gaps. 


127 


lated  so  that  the  adjustment  can  be  made  while  the  coil 
or  transformer  is  in  operation.  This  form  of  gap  can 
easily  be  muffled  by  placing  a  large  glass  jar  over  it,  thus 
excluding  the  noise,  or  can  be  cooled  by  allowing  a  small 
fan  to  blow  on  to  it,  if  desired. 

A  series  gap  is  shown  in  fig.  40,  which  gives  a  smooth 
spark  with  many  desirable  features.  It  can  readily  be 
constructed  in  a  desired  size  by  referring  to  the  figure. 
Too  much  care  cannot  be  taken  to  insulate  the  electrodes 
well,  and  to  provide  large,  true  surfaces  on  the  gap  elec- 
trodes. While  only  a  single  dead  electrode  is  shown  in 
the  figure,  two  or  more  dead  electrodes  may  be  used  if 


FIG.-4D. 


RE. 


the  sending  coil  or  transformer  is  large.  The  electrode 
faces  are  made  preferably  of  copper  sheet,  with  perfora- 
tions as  shown  to  prevent  uneven  wear  and  made  detach- 
able as  shown  so  that  they  can  be  cleaned  or  renewed. 
This  type  of  gap  has  a  large  cooling  surface  and  is  to 
be  commended  for  experimental  use.  The  relative  dis- 
tances of  the  electrodes  should  be  adjustable,  but  each 
part  of  the  gap  should  be  of  uniform  length.  The  total 
length  of  all  the  gaps  should  be  about  the  same  as  would 
be  used  in  a  single  gap. 

The  rotary  spark  gap  is  perhaps  the  most  desirable 
of  all  the  open  discharge  gaps  and  should  be  adopted 


128 


Experimental  Wireless  Stations. 


whenever  possible.  Its  advantages  are  many,  among 
which  may  be  mentioned  its  high  spark  frequency,  (the 
discharge  spark  is  broken  up  into  a  series  of  uniform 
sparks,  which  increase  the  effective  transmission  range), 
the  well  cooled  electrodes,  the  uniform  sparks,  and  others. 
There  are  many  types  and  constructions  for  rotary  gaps 


Holes 


and  while  some  of  these  are  quite  complicated,  the  reader 
will  have  little  difficulty  in  constructing  an  efficient,  in- 
expensive gap.  A  suitable  construction  is  shown  in  fig. 
41,*  and  while  numerous  variations  may  be  used,  this  form 


*This  is  not  a  hard  and  fast  design,  however,  as  many 
others  are  suitable. 


Spark  Gaps.  129 


will  prove  satisfactory  in  most  cases.  The  revolving 
electrode  as  well  as  the  stationary  electrodes  should  be 
thoroughly  insulated  from  each  other  and  foreign  bodies. 
The  revolving  electrode  should  be  insulated  from  the 
drive  shaft  or  motor.  This  is  best  accomplished  by  using 
a  three-eighths  inch  shaft  and  bearing  for  the  revolving 
electrode  and  making  connection  with  the  motor  shaft  by 
an  insulated  coupling,  such  as  is  used  in  electric  light 
fixtures.  These  couplings  may  be  had  for  a  few  cents. 
Another  simple  method  is  to  use  quite  a  long  belt  between 
the  motor  and  a  pulley  on  the  rotary  electrode  shaft.  The 
motor  used  may  be  an  ordinary  small  battery  motor  or  a 
small  synchronous  motor,  preferably  the  latter.  Fan  mo- 
tors are  desirable  for  this  purpose  and  the  power  need 
not  be  large,  since  the  rotary  electrode  offers  very  little 
if  any  greater  resistance  to  the  power  than  a  small  fan. 
The  stationary  electrodes  need  no  further  comment  and 
may  be  constructed  with  perforated  surfaces  to  make 
them  wear  out  evenly,  as  has  been  described  for  the 
series  gap.  This  perforated  feature  may  also  be  embodied 
in  the  rotary  electrode.  The  rotary  electrode  is  preferably 
made  out  of  thick  sheet  aluminum,  one-fourth  of  an  inch 
being  a  suitable  thickness.  The  size  of  the  rotary  elec- 
trode can  be  from  four  to  ten  or  more  inches  in  diameter, 
depending  on  the  power  to  be  used.  An  eight  inch  ro- 
tary electrode  is  a  convenient  size  and  may  be  used  for 
stations  up  to  ^  K.  W.  or  more.  To  make  this  electrode, 
proceed  as  follows : 

CONSTRUCTION. 

Find  the  center  of  a  square  sheet  a  trifle  larger  than 
the  desired  diameter  and  with  it  as  a  radius  draw  three 
circles.  The  outside  circle  will  be  for  the  finished  dia- 


130  Experimental  Wireless  Stations. 

meter  of  the  electrode,  or  eight  inches  in  this  case.  The 
next  circle  will  be  a  distance  nearer  the  center,  depending 
on  the  size  of  the  electrode  In  this  case  a  circle  with  a 
three  inch  radius  will  be  used.  The  inner  circle  will  be 
the  size  of  the  shaft  used,  or  three-eighths  of  an  inch  in 
this  case.  Now  the  circle  on  the  three  inch  radius  is 
divided  into  eight  parts  by  means  of  dividers,  and  these 
points  are  prick  punched.  Eight  holes,  each  \l/2  inch 
in  diameter,  are  to  be  drilled  at  these  points,  either  before 
or  after  the  plate  is  turned  down  to  the  outside  diameter. 
This  size  of  hole  leaves  sufficient  surface  to  care  for 
power  up  to  three-fourths  of  a  kilowatt.  The  aluminum 
plate  should  be  placed  in  a  lathe  and  the  shaft  hole  drilled 
out.  The  outside  diameter  should  also  be  turned  out. 
Aluminum  should  be  worked  slowly.  Use  plenty  of  ker- 
osene oil.  In  drilling  the  holes,  care  should  be  taken  to 
drill  them  true.  It  is  advisable  to  trim  the  outer  dia- 
meter after  the  plate  has  been  placed  on  a  mandril.  The 
simple  bearings  and  mountings  need  no  further  comment. 
The  stationary  electrodes  should  have  a  face  diameter  of 
five-eighths  of  an  inch  each,  and  should  be  mounted  so 
that  they  are  at  the  center  of  the  electrode  holes  when 
at  that  position.  The  electrode  should  be  mounted  so 
that  its  face  runs  without  wobbling.  If  a  lathe  is  not 
available,  a  machinist  can  be  found  to  do  the  work  for 
you.  The  rotating  electrode  should  be  mounted  in  firm 
bearings  to  avoid  undesired  vibration. 

Note. — The  drawing  is  not  to  scale.  The  extra  bear- 
ing can  be  dispensed  with  and  the  rotary  electrode  con- 
nected direct  to  the  motor  shaft,  using  an  insulated  coup- 
ling as  a  connector.  In  the  rotary  gap  the  sparking  dis- 
tance is  best  when  it  is  relatively  short.  If  this  is  not 
maintained  as  a  short  space,  it  will  be  necessary  to  use 
less  capacity  in  the  transmitting  condenser.  This  last 


Spark  Gaps.  131 


is  not  desirable,  since  the  capacity  in  small  stations  is 
seldom  any  too  large.  Rotary  gaps  have  a  further  ad- 
vantage in  that  they  care  for  heavy  discharges  without 
heating.  Synchronous  gaps  are  those  rotated  by  means 
of  a  synchronous  motor  or  those  attached  directly  to 
the  generator  shaft  so  that  sparks  occur  in  accordance 
with  the  alternations  of  the  supply  current.  Perfectly 
pure  tones  are  produced  in  this  manner.  This  is  not  al- 
ways possible  when  the  gap  is  not  driven  synchronously. 
With  small  aerials,  the  rotary  gap  allows  larger  quantities 
of  energy  to  charge  the  antenna  circuit. 

The  rotating  electrode  should  be  revolved  at  a  high 
rate  of  speed,  that  resulting  from  a  direct  connection 
to  a  synchronous  motor  being  suitable.  The  gap  need 
only  be  rotated  when  in  use,  and  may  be  stopped,  while 
receiving,  if  desired. 

A  makeshift  rotary  gap  can  be  made  by  driving  evenly 
spaced  brass  headed  tacks  or  screws  into  a  wood  disk 
mounted  on  a  shaft  and  used  as  the  gap  just  described. 
Just  before  the  tacks  are  driven  down,  a  twisted  wire 
should  be  run  between  them  for  a  continuous  connection. 
This  gap  is  not  recommended  for  other  than  very  small 
outfits,  and  then  only  as  an  experiment.  The  reader  can 
doubtless  make  a  more  substantial  modification  along  the 
same  lines. 

GAPS,  IN  GENERAL. 

The  surface  of  the  electrodes  should  always  be  kept 
clean  and  bright.  Emery  cloth  is  useful  for  this  purpose, 
but  after  the  faces  have  become  worn  and  pitted,  new 
electrodes  should  be  used.  Many  makeshift  gaps  are 
easily  arranged  for  emergency  or  experimental  purposes. 
Thus  ordinary  nails,  dry  battery  zincs,  brass  pipes,  and 


132  Experimental  Wireless  Stations. 

other  similar  metallic  pieces  can  be  mounted  and  used. 
Common  porcelain  insulators  may  be  used  for  insulating 
standards.  However,  the  reader  is  advised  to  make  a 
substantial  efficient  gap,  whenever  possible. 

It  is  interesting  from  the  experimental  standpoint  to 
enclose  a  spark  gap,  preferably  one  of  the  series  type,  in 
an  air  tight  container  provided  with  an  ordinary  bicycle 
valve.  Compressed  air  from  a  tire  pump  or  carbon  dioxid 
from  a  Presto  tube  can  then  be  used  to  increase  the  num- 
ber of  molecules  present  between  the  electrodes,  and 
under  certain  conditions  surprisingly  good  results  may 
be  obtained. 

The  reason  why  a  high  spark  rate  is  desirable  is  that 
it  can  be  distinguished  and  read  better  than  the  ordinary 
discharge,  and  that  the  individual  discharges  have  an 
additive  effect  in  the  receiver,  building  up  a  charge  which 
results  in  a  good  signal.  An  ordinary  discharge  does  not 
have  this  building  effect  upon  the  receiver,  because  the 
initial  impulse  is  the  actuating  force.  The  subsequent 
impulses  resulting  from  the  charge,  die  out  rapidly  with- 
out materially  affecting  the  receiving  signal  All  the  com- 
mercial stations  have  adopted  a  high  spark  rate  in  one 
form  or  another,  the  rotary  gap  being  quite  generally 
used.  The  few  which  have  not  adopted  high  spark  rates 
are  the  old  style  commercial  stations,  some  of  which  are 
not  even  as  good  as  the  up-to-date  experimental  stations. 


CHAPTER  XL 


RADIATION    INDICATORS.  — HOT    WIRE    AM- 
METER.—SHUNT  RESONATOR.— WAVE 
METER. 

A  radiation  indicator  is  a  device  which  indicates  when 
the  aerial  is  radiating  the  maximum  amount  of  energy. 
It  is  essential  to  accurate  effective  wireless  work,  and  is 
used  to  indicate  when  the  circuits  are  in  resonance.  There 
are  two  types  -to  be  described  here  as  standards.  The 
first,  the  hot  wire  ammeter,  is  recommended.  The  shunt 
resonator  is  perhaps  a  little  easier  to  construct,  but  is 
less  reliable  to  use.  In  addition  to  the  methods  described, 
there  is  an  instrument  called  a  wave  meter,  which,  while 
readily  constructed,  (it  is  a  simple  condenser  and  induct- 
ance of  known  dimensions),  is  unsuited  to  experimental 
use,  because  it  is  practically  useless  unless  accurately 
calibrated.  While  this  can  be  approximated  by  calcula- 
tions, this  method  is  tedious  and  unreliable.  However, 
if  a  calibrated  wave  meter  can  be  had  for  comparison,  the 
reader  is  advised  to  construct  a  wave  meter  and  calibrate 
it  by  comparison  with  the  known  standard,  which  is  very 
simple.  It  may  be  remarked  that  almost  any  form  of 
variable  condenser  can  be  used  for  the  capacity  and  that 
a  few  turns  of  bell  wire  wound  on  a  form  about  nine 
inches  in  diameter  will  do  for  the  inductance.  A  tele- 
phone receiver  and  a  detector  serve  to  indicate  well 


134  Experimental  Wireless  Stations. 

enough  for  experimental  purposes.*  In  practice  this  in- 
strument is  placed  so  that  the  inductance  is  in  a  parallel 
plane  to  the  sending  helix  or  oscillation  transformer.  (See 
fig.  42.)  It  should  not  be  placed  too  near,  however,  a  dis- 
tance of  a  few  feet  being  desirable.  Now>  to  find  the 
primary  wave  length  with  this  device,  the  arrangement  is 
as  shown  at  (a)  with  the  aerial  and  ground  out  of  the 
circuit.  The  capacity  of  the  wave  meter  is  varied  until 
the  telephone  receiver  indicates  a  maximum  point.  The 
wave  length  of  the  circuit  measured  is  then  very  nearly 
the  same  as  that  indicated  by  the  calibrated  wave  meter. 
The  operation  is  essentially  a  comparison  of  a  known 
wave  length  with  an  unknown  one.  The  readings  should 


W«««  M.t.r 


be  taken  with  different  turns  of  the  helix  in  the  primary 
circuit  until  the  wave  length  for  the  different  amounts 
of  inductance  is  ascertained.  The  wave  length  for  the 
aerial  circuit  is  obtained  in  the  same  way,  the  condenser 
being  disconnected  as  shown  at  (b).  The  wave  length 
using  different  amounts  of  inductance  in  the  antenna  cir- 


*A  calibrated  shunt  resistance,  (as  described  on  p. 
180)  may  be  used  about  the  telephone  receiver  of  the 
wave  meter,  and  will  materially  aid  accurate  work. 


Radiation  Indicators. 


135 


cuit  is  then  determined.  In  practice  the  two  circuits  arc 
connected,  so  that  both  the  aerial  and  condenser  circuits 
are  at  the  same  wave  length.  Thus  if  the  condenser  cir- 
cuit gives  a  wave  length  of  200  meters  with  one  turn  of 
the  helix  and  the  aerial  circuit  gives  a  wave  length  of 
200  meters  by  itself  when  4l/2  turns  are  in  circuit,  the 
connections  should  be  made  in  this  ratio.  If  the  primary 
wave  length  is  increased  or  decreased,  the  secondary  or 
antenna  wave  length  must  be  changed  accordingly. 

The  hot  wire  ammeter  is  used  in  a  somewhat  different 


Hot  WiW    Meter 


FIC.43.  T 


—  G 


RE. 


manner.  The  indicator  of  the  meter  is  operated  by  the 
expansion  and  contraction  of  a  fine  wire  according  to 
the  strength  of  the  oscillatory  current  which  passes 
through  it,  a  maximum  current  causing  a  maximum  de- 
flection of  the  pointer.  This  meter  is  connected  either  in 
the  aerial  or  ground  conductor  and  is  connected  directly 
in  circuit.  After  the  adjustments  have  been  made,  it  is 
preferably  short  circuited  or  removed  as  its  resistance 
impedes  the  oscillations  to  some  extent.  The  connections 
are  shown  in  fig.  43.  Now,  since  with  a  standard  experi- 


136  Experimental  Wireless  Stations. 

mental  outfit,  the  primary  or  condenser  circuit  is  to  oper- 
ate at  a  wave  length  of  200  meters,  and  the  proper  rela- 
tions are  found  by  calculation,  the  hot  wire  meter  will 
be  used  to  bring  the  secondary  or  antenna  circuit  into 
resonance  with  the  primary  circuit,  and  also  to  indicate 
the  proper  adjustment  for  the  spark  gap.  To  operate 
then,  connect  the  hot  wire  meter  in  the  aerial  or  ground 
lead,  and  close  the  primary  current.  The  condenser  and 
inductance  of  the  primary  circuit  are  left  so  that  they 
fprm  a  circuit  having  a  wave  length  of  200  meters  ac- 
cording to  the  calculations,  and  the  aerial  helix  clip  is 
placed  at  some  arbitrary  point  on  the  helix.  The  deflec- 
tion of  the  meter  should  be  noted.  Different  amounts 
of  the  helix  are  then  connected  in  the  aerial  circuit  until 
a  maximum  deflection  is  obtained,  indicating  that  the 
circuits  are  in  resonance  or  nearly  so.  For  a  wave  length 
of  two  hundred  meters,  the  contact  points  should  always 
remain  at  this  point  and  the  capacity  in  the  condenser 
circuit  should  not  be  changed.  If  the  primary  conden- 
ser is  made  larger  or  smaller,  the  whole  tuning  operation 
will  have  to  be  repeated  again.  Now  leaving  the  rest 
of  the  circuits  fixed,  adjust  the  length  of  the  spark  gap 
until  the  meter  indicates  a  maximum  deflection.  With 
this  done,  the  station  is  reasonably  sure  to  be  well  tuned, 
and  if  there  are  no  other  troubles,  such  as  leaks,  short 
circuits,  or  brush  discharges,  the  station  is  sure  to  radiate 
efficiently  at  the  given  wave  length.  Increased  or  de- 
creased wave  lengths  may  be  obtained  by  changing  the 
amount  of  the  primary  inductance,  re-calculating  the 
primary  wave  length  with  the  new  amount  of  inductance, 
and  repeating  the  tuning  operation  with  the  wire  meter 
until  the  secondary  circuit  is  again  in  resonance.  The 
spark  gap  need  not  be  changed  unless  the  capacity  is 
varied,  which  is  not  recommended  after  the  proper  rela- 


Radiation  Indicators.  13? 

tions  of  the  circuit  are  once  found.  Experiment  will 
doubtless  show  that  there  is  one  wave  length  or  range  of 
wave  lengths  which  will  produce  a  greater  deflection  of 
the  meter  than  the  others  at  resonance  and  if  this  does 
not  greatly  exceed  200  meters  it  may  be  used,  though  the 
adjustment  which  gives  a  wave  length  of  200  meters  or 
very  nearly  200  meters,  with  a  maximum  deflection  at 
that  point,  is  to  be  preferred.  When  a  loading  coil  is 
used  for  long  wave  lengths  a  similar  plan  is  used,  the 
loading  coil  being  regarded  as  an  extension  to  the  sec- 
ondary inductance. 

CONSTRUCTION  OF  A  HOT  WIRE  AMMETER. 

A  hot  wire  meter  need  not  be  a  complicated  piece  of 
apparatus,  since  essentially  it  comprises  a  mechanical 
movement  which  will  indicate  the  contraction  and  expan- 
sion of  a  fine  wire  through  which  the  oscillatory  cur- 
rent passes.  The  sensitive  part,  then,  is  the  bearing  and 
arrangement  of  the  movement.  The  balance  wheel  of 
an  old  alarm  clock  is  suitable  for  this  purpose. 

In  taking  the  balance  wheel  and  hair  spring  out  of 
the  old  clock,  leave  enough  of  the  framework  to  hold  it 
together.  This  is  all  that  is  wanted  from  the  clock  and 
the  remainder  of  the  frame  should  be  cut  away  with 
some  heavy  tin  shears.  It  is  well  to  clean  the  bearing 
out  and  oil  the  latter. 

Mount  the  balance  wheel  with  its  bearings  in  a  wooden 
frame,  8  inches  long,  5  inches  high  and  2J/2  inches  deep 
as  shown  in  the  figures,  44  to  46.  The  frame  should  be 
neatly  and  strongly  made.  The  balance  wheel  should 
be  mounted  at  the  center  of  the  bottom  piece 

Put  the  balance  wheel  spring  into  tension  by  rotating 
the  wheel  a  few  turns. 

Obtain  a  short  piece  of  silk  thread  (size  A  or  O  is 


138 


Experimental  Wireless  Stations. 


suitable),  and  after  fastening  it  to  the  balance  wheel, 
wind  it  five  times  around  the  axle  of  the  wheel.  The 
winding  should  be  arranged  so  that  the  pull  of  the  spring 
under  tension  is  checked  by  holding  the  thread.  That  is, 
the  thread  should  be  wound  in  a  direction  which  will 
maintain  the  tension  of  the  wound  up  spring. 

The  hot  wire  itself  is  made  from  a  small  piece  of 
No.  36  B&S  bare  platinum,  resistance,  or  copper  wire, 


Dial  Space 


FIE. 45 


Del-oils. 


FIG.4B 


FIG.44- 


RE. 


preferred  in  the  order  named.  Nichrome  or  climax  re- 
sistance wire  serves  very  well  for  experimental  purposes 
and  copper  wire  will  do.  Stretch  this  wire  between  the 
two  binding  posts  P  and  PI,  so  that  it  is  in  a  plane  above 
the  point  where  the  silk  thread  is  wound  on  the  axle. 
This  will  be  clear  from  the  illustrations.  Either  P  or  P' 
should  be  made  adjustable  so  that  the  tension  of  the  wire 
can  be  adjusted.  This  adjustment  is  necessary  to  counter- 


Radiation  Indicators.  139 

act  the  natural  expansion  or  contraction  of  the  wire  un- 
der varying  weather  conditions. 

The  pointer  can  be  made  either  from  a  thin  piece  of 
aluminum  sheet  or  a  small  piece  of  wood.  This  pointer 
should  be  made  very  light  and  is  made  Zl/2  inches  long. 
The  cross  section  of  the  pointer  should  not  exceed  one- 
sixteenth  of  an  inch  by  one  thirty-second  of  an  inch,  as 
it  is  essential  to  have  a  very  light  pointer.  If  this  pointer 
is  painted  black  the  readings  will  be  facilitated. 

To  fasten  the  pointer,  pull  the  thread  so  that  the 
spring  is  under  tension  and  fasten  one  end  of  the  pointer 
to  one  of  the  spokes  of  the  balance  wheel  by  means  of 
a  piece  of  No.  36  wire  or  of  the  silk  thread  left  frcm 
the  other  parts..  A  drop  of  hot  wax  or  glue  will  serve  to 
make  the  joint  rigid.  When  fastened,  the  pointer  should 
be  in  line  with  the  center  of  the  wheel. 

The  dial  can  be  made  on  a  piece  of  stiff  paper  and 
should  be  placed  close  to  the  back  of  the  pointer  so  that 
it  does  not  interfere  with  its  movement.  The  divisions 
on  the  scale  may  be  any  desired  number  and  are  used 
only  for  comparative  readings.  Commercial  instruments 
are  generally  calibrated  direct  in  amperes  or  parts  of  an 
ampere,  but  for  experimental  purposes,  comparative  read- 
ings are  all  that  are  necessary.  The  dial  should  be  of 
a  size  which  will  co-operate  with  the  pointer  and  should 
be  placed  so  that  its  center  point  is  directly  above  the 
center  of  the  balance  wheel. 

In  putting  the  parts  together,  place  the  scale  in  posi- 
tion first,  and  tie  the  silk  thread  to  the  No.  36  wire 
at  its  middle  point  so  that  the  pointer  is  moved  to  the 
0  point  of  the  scale.  A  gtass  cover  and  a  suitable  back 
can  then  be  provided,  making  a  neat  instrument.  This 
meter  will  give  comparatively  large  readings  for  small 
stations,  and  if  large  power  is  used  the  fine  wire  should 


140  Experimental  Wireless  Stations. 

be  shunted  with  a  coil  of  No.  26  or  28  copper  wire.  This 
coil  can  be  wound  on  a  pencil  and  the  amount  of  wire 
needed  must  be  found  by  experiment.  If  this  shunt  is  not 
provided,  large  coils  or  transformers  will  burn  the  fine 
wire  out.  A  good  plan  is  to  start  with  only  one  or  two 
turns  in  shunt  and  if  the  meter  is  not  operated,  add  more 
turns  until  the  proper  amount  is  found.  Part  of  the  cur- 
rent goes  through  the  shunt  so  that  the  fine  wire  is  not 
overloaded. 

When  an  oscillatory  current  passes  from  P  to  PI  the 
fine  wire  is  heated  and  in  expanding  it  leaves  a  slack  in 
the  silk  thread  which  is  taken  up  by  the  tension  of  the 
spring. 

This  causes  the  axle  to  wind  up  so  that  the  balance 
wheel  and  pointer  move.  On  account  of  the  small  dia- 
meter of  the  axle  and  the  large  leverage  of  the  pointer, 
a  very  small  movement  of  the  thread  makes  a  large  move- 
ment of  the  pointer.  When  the  wire  is  cooled,  it  contracts 
again  and  draws  the  pointer  back  to  zero.  It  will  always 
return  to  zero  when  the  wire  cools  again,  and  if  it  does 
not  on  account  of  weather  conditions,  the  wire  may  be 
adjusted  by  either  P  or  PI  (made  adjustable)  so  that 
it  does. 

The  dimensions  given  need  not  necessarily  be  adhered 
to  as  long  as  the  general  principle  is  recognized  and  used. 
By  using  the  balance  wheel  and  hair  spring  of  a  watch 
with  its  delicate  bearings,  a  much  smaller  and  sensitive 
instrument  can  be  made.  In  this  case,  a  finer  wire  should 
be  used,  No.  40  being  suitable  for  an  ordinary  watch 
spring.  The  remainder  of  the  instrument  should  be  cor- 
respondingly small,  particular  care  being  taken  with  the 
pointer. 

The.  success  of  this  instrument  depends  largely  on 
the  care  taken  in  its  construction,  and  though  very  simple, 


Radiation  Indicators.  141 

it  should  be  regarded  as  a  delicate  instrument.  The  cas- 
ing may  be  made  round  or  any  other  shape  and  can  be 
of  metal  if  the  parts  are  well  insulated  from  each  other 
and  the  metal. 

The  hot  wire  ammeter  is  very  desirable  because  it 
indicates  the  maximum  radiation  better  than  any  other 
simple  apparatus.  While  the  wave  meter  does  this  to  a 
certain  extent,  its  use  is  limited  to  the  actual  measure- 
ment of  wave  lengths  and  is  not  very  useful  in  determin- 
ing the  maximum  radiation. 

CONSTRUCTION  OF  A  SHUNT  RESONATOR. 

This  arrangement  acts  as  a  radiation  indicator  and 
serves  the  same  purpose  as  the  hot  wire  meter  except 
that  it  is  less  delicate  and  sensitive  in  its  indications.  It 
has  the  advantage  of  not  interfering  with  the  oscillations 
and  can  be  left  in  circuit  continually.  The  arrangement 
is  shown  in  fig.  47.  The  coil  is  constructed  like  a  helix, 
about  a  dozen  turns  of  No.  8  wire  wound  on  a  form  three 
inches  in  diameter  and  spaced  one-fourth  inch  apart,  with 
a  movable  contact,  being  suitable.  The  lamp  used  is  a 
small  four  or  six  volt  carbon  filament  bulb,  and  may  be 
had  at  any  supply  house.  Whenever  the  transmitter  is 
in  operation  the  lamp  lights  up. 

The  coil  is  connected  as  shown  in  shunt  around  six  or 
more  feet  of  the  ground  wire,  the  proper  amount  to  be 
determined  by  experiment.  Only  a  part  of  the  high  fre- 
quency current  is  passed  through  the  coil  by  this  arrange- 
ment so  that  the  resistance  of  the  ground  wire  is  not  in- 
creased. It  is  really  decreased  to  some  extent.  The 
effect  is  probably  due  to  the  resonant  relation  of  the  coil 
and  the  section  of  the  ground  wire. 

To  find  the  maximum  radiation  at  a  desired  wave 
length,  place  the  slider  of  the  indicator  coil  so  that  all 


142 


Experimental  Wireless  Stations. 


the  turns  are  in  circuit  and  adjust  the  antenna  circuit 
until  the  lamp  lights  up  the  brightest.  Now  decrease  the 
number  of  turns  on  the  indicator  coil,  thus  decreasing 
the  brilliancy  of  the  lamp,  and  adjust  the  transmitting 
circuits  again.  Continue  this  process  until  the  lamp  lights 
up  brilliantly  with  the  least  possible  number  of  turns  of 
the  indicator  coil  connected  in  circuit.  The  transmitting 
station  will  then  have  a  maximum  radiation  for  a  given 
wave  length.  A  similar  arrangement  can  doubtless  be 


FIE-47 


used  by  substituting  a  hot  wire  meter  for  the  lamp,  in 
which  case,  the  radiation  can  be  read  directly.  This  is 
likely  to  be  hard  on  the  meter,  however.  Credit  for  this 
shunt  indicator  with  a  lamp  is  due  to  Mr.  A.  S.  Hickley. 
We  have  now  considered  the  transmitter  and  its  sev- 
eral details  in  some  degree  of  thoroughness,  paying  par- 
ticular attention  to  the  resonant  relations  of  the  circuits 
and  the  design  of  standardized  instruments.  It  is  well 
to  again  remind,  that  all  of  the  circuits  should  be  well 
connected,  contact  points  clean  and  of  even  surface,  spark 


Radiation  Indicators.  143 

gaps  clean  and  properly  adjusted,  and  everything  ar- 
ranged in  as  workmanlike  and  businesslike  a  manner  as 
is  possible.  Too  much  emphasis  can  hardly  be  placed  on 
the  necessity  for  sharply  tuned  resonant  apparatus  pre- 
ferably operated  at  a  low  wave  length. 

A  word  as  to  cost.  The  cost  of  a  station  depends 
largely  on  the  individual.  Some  experimenters  are  able 
to  construct  and  operate  efficient  sets  which  cost  only  a 
few  dollars  while  other  less  experienced  or  less  fortunate 
workers  may  spend  many  times  as  much  without  better 
or  even  as  good  results  The  author  believes  that  a  good 
250  watt  station  to  operate  at  a  wave  length  of  200 
meters  can  be  constructed  at  an  average  cost  of  about 
$25  for  the  transmitter,  though  the  actual  figures  may 
be  considerable  more  or  less  in  each  case,  according  to 
the  circumstances  involved.  This  figure  does  not  con- 
sider the  item  of  labor,  transportation  charges  and  many 
other  variable  factors,  and  indicates  little  more  than  the 
cost  of  the  materials  used.  While  larger  stations  (larger 
power)  do  not  necessarily  follow  in  the  same  ratio,  the 
expense  may  be  taken  roughly  as  an  additional  $20  for 
every  150  additional  watts.  This  amount  is  not  to  be 
taken  as  fixed  or  even  accurate,  as  there  are  so  many 
variable  factors  concerned.  As  an  example,  the  hot  wire 
meter  described  in  this  chapter  will  be  made  by  many 
readers  at  a  total  expense  of  less  than  25c,  while  others 
will  doubtless  spend  up  to  a  few  dollars  in  its  construc- 
tion. In  general,  then,  it  is  well  to  make  the  several  parts 
as  substantial  and  neat  as  possible  without  an  excessive 
expenditure.  After  all,  the  "Works  are  more  important 
than  the  looks,"  though  good  appearance  is  also  desirable. 
Receiving  stations  can  be  made  at  a  cost  of  perhaps  75c 
or  up  to  as  much  as  you  wish.  Designs  for  receiving  ap- 
paratus will  be  found  in  later  chapters. 


144  Experimental  Wireless  Stations. 

The  need  of  thorough  insulation  throughout  is  per- 
haps most  important  of  all  and  all  insulation  should  be 
quite  thick  in  order  to  avoid  the  dielectric  effect.  In  wire- 
less transmission,  a  great  deal  of  energy  may  pass  through 
an  insulator  to  a  foreign  body  on  account  of  the  capa- 
city which  is  formed.  Thick  insulation  cuts  down  the 
capacity  and  consequently  avoids  this  effect.  With  reso- 
nant, well  adjusted  circuits  and  a  well  insulated  aerial, 
very  good  results  may  be  expected.  In  fact  with  these 
precautions  observed  better  results  may  often  be  had 
from  a  small  outfit  than  from  a  much  larger  outfit  in 
which  the  several  points  are  not  well  carried  out. 

ACCURATE  MEASUREMENTS— FREQUENCY. 

Although  many  who  read  this  volume  are  not  directly 
concerned  with  accurate  measurements  in  radio  work  it 
seems  well  to  mention  that  one  can  determine  a  wealth  of 
facts  by  using  the  wavemeter,  the  hot  wire  ammeter,  or 
both.  Knowing  the  wave  length  for  instance  one  can 
immediately  determine  the  frequency  of  the  oscillations 
in  the  aerial.  Thus  frequency  equals  1,000  million  di- 
vided by  wave-length  in  feet.  A  wave  length  of  10.000 
feet  (nearly  two  miles)  for  example  means  that  the  fre- 
quency is  only  100,000  and  it  is  evident  that  lower  wave- 
lengths mean,  under  like  conditions,  higher  frequencies. 
Other  quantities  such  for  instance  as  the  decrement  can 
also  be  obtained  with  accuracy  and  facility. 


CHAPTER  XII. 


CONTINUOUS  WAVES.  WIRELESS  TELEPHONE. 

QUENCHED  SPARK.    HIGH  FREQUENCY 

ALTERNATORS. 

The  more  advanced  methods  of  wireless  communica- 
tion utilize  continuous  waves,  produced  either  by  an  arc, 
quenched  spark,  or  direct  high  frequency  generator.  In- 
asmuch as  these  methods  are  quite  likely  to  be  developed 
into  the  ultimate  perfected  wireless  system,  some  con- 
sideration of  the  theory  together  with  experimental  opera- 
tion is  worthy  of  attention. 

A  simple  system  that  may  be  used  for  telegraphy  or 
telephony  is  shown  in  fig.  48.  This  arrangement  will 
only  operate  on  direct  current  of  1 10  or  220  volts,  prefer- 
ably the  latter.  The  power  supply  should  be  capable  of 
furnishing  a  uniform  current  of  10  amperes.  The  arc 
light  may  be  an  ordinary  arc,  but  the  lower  electrode  is 
preferably  made  of  brass  or  copper  and  water  cooled. 
This  water  cooled  electrode  may  easily  be  made  from  a 
plumber's  T  connection,  using  a  brass  plug  for  the  elec- 
trode end.  Rubber  tubing  can  be  used  to  connect  the 
T  to  a  water  supply.  The  arrows  indicate  the  flow. 
The  aerial,  ground  and  oscillation  transformer  may  be  the 
same  as  for  the  spark  system  already  described.  The 
condenser  should  be  variable,  as  the  exact  amount  of 
capacity  must  be  found  by  experiment.  A  hot  wire  meter 
in  the  aerial  can  be  used  to  indicate  the  correct  adjust- 
ment of  the  circuits.  The  impedance  coil  is  made  by 


146 


Experimental  Wireless  Stations. 


forming  an  iron  core  \l/2  in.  square  and  5x8  in.  outside 
dimensions,  as  for  a  transformer,  winding  about  four 
pounds  of  No.  12  D.  C.  C.  wire  on  the  long  legs.  The 


purpose  of  the  impedance  coil  is  to  prevent  the  oscillations 
from  surging  back  into  the  generator.  The  choke  coil 
is  made  similar  to  the  impedance  coil,  except  that  only 


Continuous  Waves — Advanced  Systems.        147 

two  pounds  of  wire  are  used  and  wound  on  one  leg.  If 
desired,  a  secondary  can  be  wound  on  the  other  leg.  (See 
chapter  on  transformers.)  A  resistance  for  the  arc  should 
also  be  provided.  This  may  be  made  by  placing  two  elec- 
trodes an  adjustable  distance  apart  in  a  solution  of  salt 
and  water.  A  transmitter  or  a  key  can  be  shunted  around 
the  choke  coil,  according  to  the  use  to  be  made  of  the 
set,  or  the  key  or  transmitter  may  be  used  to  vary  other 
parts  of  either  the  primary  or  aerial  circuit.  A  current 
through  the  secondary  winding  of  the  choke  coil  may  also 
be  used  when  it  is  modified  by  a  transmitter 

It  is  understood,  of  course,  that  the  transmitter  in 
fig.  48  is  used  instead  of  a  key  when  the  circuit  is  used 
as  a  wireless  telephone,  or  vice  versa.  That  is,  a  key 
may  be  substituted  for  a  transmitter  to  form  an  experi- 
mental arc  telegraph.  If  the  key  or  transmitter  is  used 
in  the  aerial,  a  duplicate  in  the  main  arc  circuit  is  not 
needed.  For  telephone  experiments  the  transmitter  is  best 
shunted  around  the  choke  coil  as  shown  in  the  lower  in- 
sert of  fig.  48.  Only  the  choke  coil  and  transmitter  (Tr.) 
are  shown  in  this  insert,  as  the  circuit  is  the  same  in  other 
respects.  In  this  case  only  one  winding  is  used.  If  the 
two  windings  are  used  as  shown,  the  transmitter  is  con- 
nected to  the  secondary  winding  through  a  battery.  In 
this  method  the  variations  caused  by  the  transmitter  are 
superposed  on  the  line  current  by  induction  and  in  turn 
cause  variations  in  the  arc  circuit.  In  the  shunt  method 
the  transmitter  carries  part  of  the  current  directly,  while 
in  the  inductive  method  it  is  only  indirectly  connected  to 
the  main  circuit.  Ordinary  transmitters  can  be  used. 
It  is  advisable  to  use  two  or  three  connected  in  parallel 
and  grouped  as  a  single  unit.  Larger  currents  can  be 
cared  for  in  this  manner.  The  author  has  passed  from  1 
to  4  amperes  through  an  ordinary  transmitter  with  good 


148  Experimental  Wireless  Stations. 

results.  The  transmitter  was  heated  by  this  treatment, 
however,  and  in  some  later  trials,  it  was  burned  out. 
Indeed,  the  art  is  materially  hindered  at  present,  for  want 
of  a  satisfactory  transmitter. 

It  should  be  noted  that  the  oscillatory  circuit  is  formed 
by  the  condenser,  oscillation  transformer  and  arc.  The 
circuit  through  the  resistance,  impedance  coil,  arc  and 
choke  coil  is  used  to  excite  the  arc. 

In  operation,  the  condenser  is  alternately  charged  and 
discharged  at  a  very  high  rate,  because  the  voltage  be- 
tween the  arc  terminals  decreases  with  an  increase  of  tht 
current.  The  condenser  takes  current  from  the  arc,  caus- 
ing an  increase  of  the  voltage  between  the  terminals,  and 
as  a  result  more  current  flows  into  the  condenser.  Even 
after  the  condenser  is  charged  to  the  same  potential  as 
that  between  the  arc  electrodes,  the  current  in  the  con- 
denser continues  because  of  the  inductance  in  series  with 
it.  The  potential  difference  at  the  condenser  thus  becomes 
more  than  at  the  arc  terminals,  so  that  the  condenser  now 
begins  to  discharge  through  the  arc.  This  immediately 
causes  the  voltage  of  the  arc  to  drop,  so  that  the  discharge 
continues.  Finally  the  condenser  potential  falls  below 
that  of  the  arc  electrodes  and  the  process  reverses  again. 
The  condenser  continues  to  charge  and  discharge  in  this 
manner  and  the  resulting  oscillatory  current  is  utilized 
in  the  transmission.  The  arc  is  varied  by  the  transmitter 
or  key  and  in  the  former  case,  causes  the  arc  to  reproduce 
the  sounds  spoken  into  the  transmitter.  The  resulting 
oscillations  are  similarly  varied  so  that  the  receiver  gets  a 
more  or  less  exact  reproduction  of  the  transmitted  sound 
waves  which  are  sent  as  electromagnetic  waves. 

The  frequency  produced  in  an  arc  system  is  very 
high,  being  from  100,000  to  1,000,000  per  second,  and 
can  not  be  heard  by  the  receiver  except  when  modified  as 


Continuous  Waves — Advanced  Systems.        149 

by  a  transmitter.  Very  close  tuning  is  necessary  to  get 
results  from  this  circuit,  and  the  experimenter  is  quite 
safe  in  using  any  reasonable  wave  length  with  this  ar- 
rangement, since  for  telegraphic  purposes  with  a  key  used 
to  make  or  break  the  aerial  circuit,  ordinary  receiving 
stations  are  not  interfered  with.  The  Poulsen  system 
operates  along  these  lines. 

A  singing  arc  is  made  by  connecting  variable  capaci- 
ties in  the  shunt  circuit  of  the  arc.  The  pitch  varies  ac- 
cording to  the  capacity  in  this  case,  the  highest  pitch  being 
obtained  by  the  use  of  a  very  little  capacity.  If  a  tele- 
phone transmitter  is  also  used  the  arrangement  forms  a 
talking  arc.  This  is  really  a  wireless  telephone  without 
helix,  aerial  and  ground.  It  is  also  possible  to  omit  the 
condenser  for  this  purpose.  Words  spoken  into  the 
transmitter  are  reproduced  by  the  variations  in  the  arc. 
The  sound  will  be  louder  as  the  length  of  the  arc  is  in- 
creased. (Do  not  look  at  the  arc  too  much,  as  it  is  very 
bad  for  the  eyes.) 

An  arc  system  allows  very  sharp  tuning  to  be  car- 
ried out,  and  as  a  result  it  does  not  interfere  with  other 
stations,  as  much  as  ordinary  spark  sets  do.  The  per- 
sistent train  of  oscillations  produced  by  this  method  is  a 
decided  advance  in  the  wireless  art.  The  received  signal 
is  an  accumulated  impulse  resulting  from  a  series  of  the 
oscillations,  as  has  been  explained  for  the  rotary  gap. 
The  arrangement  described  will  only  operate  over  short 
distances,  however,  as  large  power  and  specially  designed 
arcs  and  apparatus  are  necessary  for  long  distance  work. 

THE  LEPEL  ARC  SYSTEM. 

This  arrangement  is  a  combination  of  the  arc  and  the 
quenched  spark  systems,  and  operates  on  either  direct  or 


150 


Experimental  Wireless  Stations. 


alternating  current  of  500  or  1,000  volts.  This  voltage 
may  be  obtained  from  an  ordinary  alternating  current 
supply  by  means  of  a  step  up  transformer.  A  five  hun- 
dred watt  step  up  transformer  with  a  ratio  of  1  to  5  will 
serve  nicely  on  110  volts  A.  C.  for  experimental  purposes. 
The  arrangement  is  very  simple  and  is  shown  in  fig.  50.* 
The  condenser  used  can  be  made  of  paraffined  paper  on 
account  of  the  low  voltage  used,  but  glass  is  recommended. 
The  remainder  of  the  apparatus  with  the  exception  of  the 
arc  or  gap  itself  is  familiar  and  needs  no  further  com- 


•" 


T«  Lint  o«4  Kty. 


FIC.5D 


Water 


Con  witK  W«t«r 
FIE. 51. 


RE. 


ment.  A  suitable  construction  for  the  gap  for  experi- 
mental purposes  is  illustrated  in  figure  51.  Ordinary  tin 
cans  can  be  utilized,  but  the  electrode  faces  should  be  of 
copper  turned  smooth  and  having  a  groove  as  shown. 
This  groove  serves  to  prevent  the  arc  from  reaching  the 
outside  of  the  gap.  These  copper  disks  should  be  from 
3  to  5  inches  in  diameter,  and  can  be  arranged,  after  the 
cans  are  filled  nearly  full  of  water.  The  two  electrodes 


*  No  chopper  is  needed  at  the  receiver  when  A.  C.  is 
used  with  the  transmitter. 


Continuous  Waves — Advanced  Systems.        151 


are  separated  by  a  circular  disk  of  paper,  not  more  than 
.01  in.  thick.    A  good  bond  paper  will  do.    The  disk 


Groove 


SECT60N. 

Gro*v%  Air  Space 

FIG.5S. 


RE:. 


should  have  a  small  hole  at  its  center  to  afford  a  starting 
point  for  the  arc.  The  construction  is  very  simple  and 
needs  no  further  comment. 


152  Experimental  Wireless  Stations. 

In  operation  the  arc  starts  at  the  center  and  gradu- 
ally burns  the  paper  away.  As  this  burning  occurs  in 
an  atmosphere  lacking  in  oxygen,  the  paper  does  not 
burn  all  up  until  after  a  number  of  hours.  It  is  essential 
to  the  arc,  that  the  distance  between  the  electrodes  should 
be  uniform  and  not  over  .01  inch,  so  that  the  arc  occurs  in 
an  atmosphere  lacking  in  oxygen.  The  products  of  com- 
bustion of  the  paper  also  aid  the  arc's  efficiency. 

The  paper  disc  can  be  renewed  after  it  is  used  up. 
This  gap  gives  practically  continuous  oscillations  and  the 
circuits  can  be  tuned  by  using  a  hot  wire  meter.  The 
use  of  the  shunt  resonator  described  in  Chapter  11  is 
advised  with  this  arrangement  as  the  spark  or  arc  is  prac- 
tically inaudible.*  This  form  of  gap  can  be  utilized  for 
telephone  purposes  in  much  the  same  manner  as  described 
for  the  arc.  Great  care  should  be  taken  in  handling  the 
circuits  as  a  shock  from  the  line  or  secondary  might 
easily  prove  fatal.  Two  or  more  of  these  gaps  may  be 
connected  in  series,  this  method  being  suitable  for  higher 
voltages.  ; 

A  somewhat  similar  arrangement  used  on  higher  volt- 
ages and  which  does  not  need  paper  renewals  is  illus- 
trated in  fig.  52. 

TELEFUNKEN  (ARCO)  QUENCHED  GAP. 

This  is  really  a  number  of  Lepel  gaps  connected  in 
series.  This  arrangement  can  be  substituted  for  the  or- 
dinary gap  of  a  spark  system.  The  discs  are  turned  ao 
shown  from  3-16  or  J4  mch  sheet  brass  to  an  ou.sid 
diameter  of  6J/2  or  7  inches  and  grooved  1  or  \l/2  inches 
in,  so  that  the  groove  is  about  3-8  of  an  inch  wide  at  the 
face.  Each  plate  is  grooved  on  one  side  in  this  manner. 


*  When  A.  C.  is  used  the  discharge  can  be  heard. 


Continuous  Waves — Advanced  Systems.        153 

The  mica  rings  used  may  be  had  at  supply  houses  and 
should  not  extend  further  in  than  1-8  inch  beyond  the 
outside  diameter  of  the  groove,  so  that  the  inside  cir- 
cumference of  the  mica  comes  within  J4  mcn  of  the  in- 
side circumference  of  the  groove.  The  groove  is  to  pre- 
vent the  spark  from  jumping  to  the  mica  as  the  latter 
becomes  a  conductor  when  heated  by  a  high  frequency 
discharge.  The  mica  rings  should  not  be  more  than  .01 
inch  thick.  The  discs  are  assembled  in  pairs  so  that 
the  grooved  faces  are  next  to  each  other,  and  washers 
are  placed  between  the  pairs  so  that  the  pairs  are  sep- 
arated by  a  distance  equal  to  the  thickness  of  one  of  the 
plates.  Thus  if  J4  mcn  plates  are  used,  the  washers  used 
should  be  J4  mcn  thick.  The  assembled  gap  may  be 
suitably  mounted  by  using  insulated  supports,  a  sufficient 
number  of  pairs  being  used  so  that  the  combined  length 
of  the  gaps  is  somewhat  less  than  the  length  of  a  single 
gap,  ordinarily  used.  When  large  power  is  used  with 
this  gap,  it  is  well  to  have  a  small  fan  blow  upon  it  to 
dissipate  the  heat  which  is  generated. 

THEORY  AND  ADVANTAGES  OF  THE 
QUENCHED  SPARK. 

The  gaps  described  are  not  difficult  to  construct  and 
operate  and  are  recommended  to  the  readers.  The  dis- 
charge is  practically  noiseless,  almost  60  per  cent  more 
efficient  than  a  common  gap,  and  produces  practically 
undamped  waves.  A  high  pitch  note,  which  increases  the 
effective  transmission  range,  is  also  produced. 

The  operation  of  the  quenched  gap  depends  upon 
the  fact  that  the  spark  quenches  itself  out  after  it  has 
made  a  few  oscillations,  allowing  the  secondary  oscilla- 
tions to  continue  freely.  The  primary  circuit  is  thus 


154  Experimental  Wireless  Stations. 

opened  so  that  it  does  not  interfere  with  the  secondary 
or  aerial  oscillations.  As  a  result  the  unwelcome  beats 
common  to  open  spark  systems  are  avoided  Returning 
to  the  parallel  case  of  a  gong,  the  quenched  spark  may 
be  compared  to  a  padded  hammer,  which  after  striking 
the  gong  (comparable  to  the  antenna  circuit  in  this  case), 
a  forceful  blow,  allows  it  to  continue  by  itself  with  a 
clear,  powerful  vibration.  The  short  spark  gap  when  well 
cooled  prevents  the  primary  from  oscillating  by  itself  after 
the  secondary  circuit  has  been  excited.  That  is,  the  spark 
is  active  only  long  enough  to  allow  the  secondary  oscilla- 
tions to  reach  a  maximum,  and  the  secondary  oscillations 
are  a  maximum  after  the  primary  oscillations  are  reduced 
to  a  minimum.  The  number  of  primary  oscillatipns  neces- 
sary for  this  ideal  operation  is  governed  by  the  degree  of 
coupling  between  the  primary  and  secondary.  It  is  de- 
sirable to  use  a  close  degree  of  coupling  with  the  quenched 
spark  for  this  reason.  The  energy  ordinarily  lost  as  heat 
in  an  ordinary  spark  gap  is  thus  conserved  and  the  wear 
on  the  primary  apparatus  is  reduced.  One  of  the  chief 
causes  of  heat  in  the  condensers  and  wear  of  the  gap  with 
an  ordinary  open  gap  is  the  useless  continuance  of  the 
energy  after  the  useful  oscillations  have  been  generated. 
The  quenched  gap.  then,  prevents  undesirable  oscillations 
from  being  set  up  in  the  primary  by  the  reaction  of  the 
secondary,  and  makes  the  resulting  radiations  have  a  sin- 
gle wave  length,  for  receiving  purposes. 

In  constructing  the  quenched  gap,  it  is  essential  that 
the  electrodes  be  pressed  with  some  force  against  each 
other.  In  the  Lepel  form  of  gap  described  the  weight  of 
the  upper  electrode  suffices,  but  in  the  form  of  Arco  gap 
described,  a  clamp  should  be  provided.  A  quenched  gap 
in  connection  with  a  resonant  outfit  as  described  in  pre- 
vious chapters  is  an  ideal  set  for  the  experimenter.  These 


Continuous  Waves — Advanced  Systems.        155 

arrangements  are  also  known  as  shock  excited  systems, 
and  are  rapidly  coming  into  increased  favor 

Note.  If  mica  is  not  obtainable  in  the  necessary  size, 
rubber  sheet  of  uniform  thickness,  .01  inch  may  be  used, 
though  the  mica  is  to  be  preferred.  Stove  repair  compa- 
nies carry  mica  in  stock  as  do  commutator  concerns.  The 
latter  use  a  mica  mixture  which  is  much  cheaper  than 
mica  and  which  is  suitable  Smaller  dimensions  may  be 
used  for  the  electrodes  for  small  stations,  and  for  very 
small  stations  one  or  two  sets  of  plates  will  suffice.  By 
using  soft  rubber  sheet  instead  of  mica  the  length  of  the 
gaps  can  be  varied  by  varying  the  pressure  on  the  plates. 
Sheets  of  soft  rubber  can  be  had  at  dental  supply  houses. 
The  quenched  gap  is  of  course  used  like  a  regular  spark 
gap  in  an  experimental  set.  Quenched  gaps  are  made  in 
both  stationary  and  rotary  forms,  the  latter  having  ad- 
vantages similar  to  those  of  an  ordinary  rotary  gap  as 
well  as  those  of  the  quenched  gap. 

The  Goldschmidt  high  frequency  generator  is  coming  into 
some  use  for  long  distance  work.  Its  operation  depends  upon 
the  fact  that  an  armature  mechanically  rotated  in  a  rotating 
magnetic  field  gives  an  initial  frequency — say  10,000 — which  can 
be  further  stepped  up  by  carrying  the  current  back  through  the 
field  to  produce  a  more  rapidly  rotating  magnetic  field;  this 
new  frequency  current  is  again  led  back  to  still  further  increase 
the  frequency,  and  so  on  until  the  desired  frequency  —  say 
40,000 — is  attained.  The  circuits  must  of  course  be  nicely  bal- 
anced electrically  in  order  to  obtain  the  necessary  resonance, 
condensers  being  used  for  this  purpose.  To  avoid  eddy  current 
losses,  the  armature  is  constructed  of  iron  foil  only  .002  inch 
thick,  each  sheet  being  insulated  from  the  next  one.  Substan- 
tially undamped  waves  are  emitted  by  the  use  of  this  machine 
and  since  the  frequency  is  above  audibility,  the  method  of  beats 
is  employed  to  get  the  intelligence  at  the  receiving  station. 

Still  another  method  for  producing  sustained  oscillations  has 
been  devised  by  Galletti.  Direct  current  is  used  as  the  primary 
source  and  a  plurality  of  oscillatory  circuits  are  automatically 
excited  in  succession,  a  common  condenser  being  coupled  to 
these  circuits.  An  experimental  alternator  has  also  been  con- 
structed by  the  Telefunken  Company  in  which  the  primary 
frequency  is  multiplied  by  means  of  a  polarised  transformer. 


CHAPTER  XIII. 


THE  RECEIVING  STATION. 

Having  considered  the  transmitter  and  its  details,  the 
receiving  station  will  now  receive  attention.  The  aerial 
and  ground  have  already  been  discussed  and  since  they 
are  the  same  in  most  cases  for  both  transmitter  and  re- 
ceiver, they  need  no  further  attention. 

We  have  seen  that  the  transmitter  emits  waves  of 
definite  lengths  and  having  definite  characteristics,  accord- 


ing  to  the  adjustment  of  the  transmitter  and  that  these 
waves  spread  out  in  all  directions  at  the  speed  of  light. 
Now  at  the  receiver,  all  that  is  necessary  is  some  appara- 
tus which  will  detect  the  waves  which  strike  the  receiving 
aerial  and  translate  them  into  an  intelligible  signal. 

For  this  reason,  the  apparatus  in  its  simplest  form 
consists  merely  of  a  detector  and  a  telephone  receiver 
connected  in  the  antenna  circuit.  This  is  shown  in  fig. 


The  Receiving  Station.  157 

53.  It  will  be  understood  that  other  sensitive  recorders 
such  as  an  Einthoven  galvanometer  can  be  used  instead 
of  the  telephone  receiver.  The  detector,  however,  is 
essential,  because  even  the  most  sensitive  telephone  re- 
ceiver or  galvanometer  cannot  record  signals  without  it. 

In  early  experiments,  a  relay  was  used  for  the  record- 
ing instrument.  In  its  most  sensitive  form,  however,  a 
relay  will  only  operate  with  about  .001  of  a  volt  at  its 
terminals.  Further,  its  action  is  slow,  so  that  it  has  been 
discontinued  for  signalling  purposes.  Its  use  is  limited 
to  the  field  of  telemechanics,  the  art  of  controlling  motors, 
boats,  etc.,  by  wireless  through  a  local  relay.  Its  co- 
operating detector,  the  coherer,  has  also  become  obsolete 
except  for  the  purpose  mentioned. 

The  telephone  receiver  is  the  instrument  in  universal 
use  for  wirelecs  receivers  and  is  the  form  to  be  adopted 
as  a  standard  for  wireless  purposes.  The  receivers  for 
wireless  purposes  are  made  different  than  for  ordinary 
purposes. 

TELEPHONE  RECEIVERS  FOR  WIRELESS 
RECEIVING. 

Receivers  for  wireless  purposes  should  be  very  sen- 
sitive. It  has  been  found  by  experiments  that  the  degree 
of  sensitiveness  depends  largely  on  the  frequency  at  which 
the  received  signals  are  sent.  Thus,  messages  from  a 
900  cycle  transmitter  will  produce  an  audible  sound  in 
the  receiver  when  only  0.6  millionths  of  a  volt  is  used, 
while  impulses  received  from  a  60  cycle  set  will  only  pro- 
duce an  audible  sound  when  620  millionths  of  a  volt  are 
used.  These  figures  are  according  to  Dr.  Austin,  and 
while  they  are  taken  for  a  particular  set  of  receivers,  with 
the  use  of  a  laboratory  arrangement,  the  general  relation 


158  Experimental  Wireless  Stations. 

holds  good.  It  is  for  this  reason  that  the  transmitters 
operating  at  500  to  1,000  cycles  are  more  effective  than 
those  operating  at  low  frequencies.  The  sensitiveness  of  a 
given  receiver,  then,  depends  on  the  frequency  employed 
to  operate  it  and  also  on  the  natural  period  of  vibration 
of  the  diaphram.  It  is  for  this  reason  that  thin  diaphrams 
are  employed  in  wireless  receivers.  The  detailed  require- 
ments for  receivers  will  receive  attention  later. 

WHY  A  DETECTOR  IS  ESSENTIAL. 

The  detector  (see  fig.  53),  is  not  of  itself  the  most 
sensitive  instrument  at  the  receiving  station,  but  in  essen- 
tial because  the  telephone  receiver,  while  more  sensitive, 
will  not  of  itself  respond  to  high  frequency  oscillations 
such  as  are  received  at  a  wireless  station.  The  reason 
should  be  apparent,  for  the  change  first  in  one  direction 
and  then  in  the  other,  of  the  oscillations  is  so  rapid  that 
the  successive  changes  neutralize  each  other  and  produce 
no  effect  in  the  receiver.  To  operate  on  these  oscillations 
a  telephone  diaphram  would  have  to  move  with  frequency 
corresponding  to  approximately  one-millionth  of  a  second, 
which  of  course  it  cannot  do.  Again,  we  have  seen  that 
high  frequency  oscillations  are  greatly  impeded  by  large 
inductance,  so  that  the  self  inductance  of  the  receiver 
would  of  itself  prevent  any  except  minute  currents  from 
operating  it.  The  detector,  then,  translates  the  received 
oscillations  into  a  current  which  will  operate  the  receiver. 

The  oscillations  coming  in  on  the  aerial  A,  fig.  53,  are 
transformed  by  the  detector  into  currents  which  operate 
the  receiver.  The  nature  of  this  transformation,  the 
construction  and  operation  of  detectors,  and  similar  mat- 
ters will  receive  attention  later. 


The  Receiving  Station.  159 

THE  RECEIVED  SIGNAL. 

The  received  signal,  then,  is  made  up  of  wave  trains 
which  set  up  an  oscillatory  current  in  the  receiving  sta- 
tion which  corresponds  to  that  sent  by  the  transmitter. 
When  it  is  remembered  that  the  transmitted  energy  is 
sent  out  in  all  directions  it  is  remarkable  that  one  point 
such  as  a  receiving  station  receives  as  much  energy  as 
it  does.  According  to  Mr.  Pickard,  measurements  of  the 
maximum  energy  received  from  a  high  power  transmit- 
ting station  90  miles  away,  showed  this  energy  to  be  .03 
ergs  per  dot.  The  "erg"  is  equivalent  to  one  ten-millionth 
of  a  watt.  Inasmuch  as  a  sensitive  telephone  receiver 
will  operate  with  an  audible  sound  on  as  little  as  one- 
millionth  of  an  erg  this  leaves  a  considerable  margin 
for  the  case  at  hand  In  any  case,  the  received  energy 
is  many  hundred  times  the  actual  energy  necessary  to 
produce  an  audible  sound  in  the  receiver,  but  since  the 
receiver  will  not  of  itself  operate  efficiently  on  the  high 
frequency  oscillations,  the  detector  employed  limits  the 
efficiency  of  the  receiving  station  to  a  large  extent. 

Like  other  transformers,  the  detector  represents  a 
source  of  loss  and  although  the  modern  detector  is  quite 
sensitive,  (see  table  p.  160),  a  detector  which  would 
be  at  least  as  sensitive  as  a  sensitive  telephone  receiver 
by  itself  would  be  of  a  great  advance  in  the  wireless  art. 

Now  the  simple  circuit  shown  in  fig.  53,  comprises  an 
untuned  receiving  set  and  is  of  little  use  without  an 
auxiliary  tuning  apparatus  if  messages  are  to  be  received 
from  modern  transmitters. 

Tuning.  In  order  to  receive  signals  from  a  trans- 
mitter, the  receiver  must  be  adjusted  so  that  its  circuits 
are  in  tune  or  resonance  with  those  of  the  transmitter. 
Thus,  if  the  receiver  is  to  receive  from  a  station  sending 


160  Experimental  Wireless  Stations. 

TABLE  OF  DETECTORS—SENSITIVENESS. 

Type  of  Detector.  Energy  required  to  operate. 

in  ergs,  per  dot. 

Electrolytic  003640— .000400  * 

.007  § 

Silicon 000430— .000450  * 

Magnetic  hysteresis  detector 01  § 

Hot-wire  barretter 0.08  § 

Carborundum  009000— .014000  * 

*  According  to  Pickard. 
§  According  to  Fessenden. 

out  a  300  meter  wave  it  must  be  adjusted  so  that  its  wave 
length  is  very  nearly  300  meters.  However,  if  the  trans- 
mitter is  poorly  tuned  or  very  close  to  the  receiver,  it 
is  a  common  occurrence  to  receive  the  message  without 
careful  tuning,  or  even  without  any  tuning.  (See  chap- 
ter on  resonance).  The  apparatus  for  tuning  a  receiver, 
consists,  as  at  the  transmitter,  of  adjustable  circuits  con- 
taining variable  capacity  and  inductance.  The  whole  sub- 
ject is  somewhat  complex  and  will  receive  individual  at- 
tention later. 

The  same  receiving  set  may  be  used  for  either  wire- 
less telegraphy  or  telephony,  since  the  conditions  are  iden- 
tical in  many  respects.  Indeed,  both  telephone  and  tele- 
graph messages  can  be  heard  at  the  same  time  in  some 
localities.  Tnis  last  is  a  special  case  of  interference. 

The  requisites  for  the  receiver  then  are : 

1.  Sensitive  detector. 

2.  Sensitive  telephone  receiver  or  recorder. 

3.  Accurate  auxiliary  adjustable  circuits  for  tuning. 

4.  A  good  aerial  and  ground,  as  for  the  transmitter. 
The  several  items  will  receive  attention  presently,  in 

some  detail. 


CHAPTER  XIV. 

DETECTORS     SOLID  RECTIFIERS. 

Quite  a  number  of  different  types  of  detectors  have 
been  discovered  and  developed  and  there  are  many  forms 
for  these.  For  the  purpose  of  standardization,  however, 
the  types  known  as  crystal  or  solid  rectifiers  are  best 
adopted  because  of  their  sensitiveness,  low  cost,  easy 
adjustment,  portability  and  durability.  Other  forms  which 
may  be  used  are  coherers,  loose  contacts,  (almost  any 
loose  contact,  as  between  a  piece  of  carbon  and  a  needle,, 
being  suitable),  magnetic  detectors,  barretters  or  thermal 
detectors,  electrolytic  detectors,  gaseous  detectors,  and 
vacuum  detectors.  Indeed,  one  might  easily  devote  an 
entire  book  to  a  consideration  of  all  types  of  detectors  and 
their  several  details.  Such  a  duplication  seems  unneces- 
sary, however,  since  solid  rectifiers  can  be  used  to  as  good 
advantage  as  the  other  types  for  all  experimental  pur- 
poses, whether  for  long  or  short  distance  receiving. 

Solid  rectifiers  consist  essentially  of  certain  metallic 
compounds,  such  as  oxides  and  sulphides,  which  have  the 
property  of  rectif  ring  the  high  frequency  oscillations. 
That  is,  these  metallic  compounds  when  connected  in  a 
circuit,  conduct  the  current  better  in  one  direction  than 
in  the  other.  This  unilateral  effect  is  quite  marked,  so 
that  the  detector  acts  as  a  valve,  allowing  the  current 
to  pass  in  one  direction  but  practically  preventing  the 
oscillation  from  completion  by  preventing  the  current 
from  passing  in  the  reverse  direction.  In  addition  to  this 


162 


Experimental  Wireless  Stations. 


property  it  is  necessary  to  have  this  rectifying  effect  car- 
ried on  regularly  so  that  the  oscillations  are  rectified  into 
a  pulsating  one  way  or  direct  current.  The  latter  then 
serves  to  operate  the  telephone  or  other  recorder.  The 
metallic  compounds  used  have  this  property  also,  so  that 
a  circuit  which  includes  a  solid  rectifier  is  a  good  detector 
for  the  wireless  receiving  circuit.  It  is  interesting  to 
note  that  while  a  part  of  this  phenomena  was  noticed  as 
early  as  1874,  these  metallic  compounds  were  not  under- 
stood and  used  as  detectors  until  about  1906.  A  partial 
list  of  the  elements  and  compounds  which  may  be  used 
for  this  purpose  are : 


Mineral  Name. 

Carborundum 

Fused  Silicon 

Iron  Pyrites 

Copper  Pyrites 

Chalcopyrites 

Hessite 

Zincite 

Octahedrite 

Stibnite 

Galena 

Molybdenite 

Zirconium 

Niccolite 

Domeykite 

Sphalerite 

Pyrrholite 

Corundum 

Hematite 

Cassiterite 

Siderite 

Malachite 

Cerusite 


Chemical  Name. 

Silicon  Carbide 

Silicon 

Iron  Sulphides 

Copper  Sulphide 

Copper  Iron  Sulphide 

Telluride  of  Silver  and  Gold 

Zinc  Oxide 

Oxide  of  Titanum 

Antimony  Sulphide 

Lead  Sulphide 

Molybdenum  Sulphide 

Zirconium 

Nickel  Arsenide 

Copper  Arsenide 

Sulphide  of  Zinc 

Iron  Sulphide 

Oxide  of  Aluminum  and  Iron 

Iron  Oxide 

Oxide  of  Tin 

Iron  Carbonate 

Copper  Carbonate 

Lead  Carbonate 


With  the  exception  of  Carborundum  these  may  all  be 
used  without  a  battery  with  good  results.    When  two 


Detectors.    Solid  Rectifiers.  163 

different  crystals  are  used  together  to  form  a  pcricon 
detector,  the  use  of  a  battery  is  optional. 

In  use,  a  small  piece  of  the  compound  which  will 
be  hereafter  called  a  crystal  for  convenience,  is  mounted 
between  two  metallic  contacts.  The  exact  nature  of  these 
contacts  depends  upon  the  particular  crystal  employed, 
and  in  nearly  every  case,  it  is  desirable  to  make  the  con- 
tacts adjustable,  so  that  the  most  sensitive  part  of  the 
crystal  can  be  used  with  the  contacts  at  the  most  sensi- 
tive pressure.  In  practically  every  case  it  is  desirable  to 
make  one  of  the  terminals  or  contacts  with  a  large  area 
so  that  it  makes  very  good  contact  with  the  crystal.  This 
is  to  prevent  the  other  contact  from  forming  an  opposing 
and  undesirable  second  rectifier,  which  would  greatly 
reduce  the  effect  of  the  former.  The  crystal  then,  is 
mounted  between  a  large  and  a  small  contact,  to  form 
an  ordinary  detector.  Silicon,  while  a  non-metallic  ele- 
ment, is  perhaps  one  of  the  most  widely  used  solid  recti- 
fiers. The  iron  pyrites  or  pyron  detector,  the  galena  or 
lead  sulphide  detector,  and  the  molybdenite  detector,  in 
the  order  named,  are  the  other  single  crystal  rectifiers 
in  most  general  use  and  favor.  Each  has  certain  advan- 
tages and  disadvantages  and  the  various  factors  which 
determine  the  utility  of  a  detector  are  so  variable  that 
direct  comparison  without  exact  comparative  tests  is  not 
possible.  In  order  to  secure  the  necessary  large  contact 
for  these  detectors,  the  crystal  is  imbedded  in  a  cup 
with  a  fusible  alloy  such  as  Woods,  metal,  (see  construc- 
tional details),  while  the  small  point  consist  of  a  rounded 
adjustable  point  of  brass,  gold,  platinum,  or  else  a  wire 
of  these  metals.  When  two  or  more  of  these  crystals, 
one  of  which  is  preferably  zincite,  are  used,  this  small 
metallic  point  is  replaced  by  a  fragment  from  another 
crystal.  A  small  piece  of  chalco-pyrite  is  generally  used 


164  Experimental  Wireless  Stations. 

for  this  purpose.  This  pericon  detector  is  perhaps  one 
of  the  best  at  present  known  as  far  as  sensitiveness, 
portability,  and  durability  are  concerned.  Small  metal 
points  are  most  suitable  for  polished  crystals  such  as  iron 
pyrites  and  galena.  These  two  detectors  are  particularly 
free  from  injury  from  mechanical  shocks  or  foreign  elec- 
trical impulses. 

For  experimental  purposes  it  is  well  to  provide  what 
is  known  as  a  universal  detector  stand  so  that  any  or  all 
of  the  materials  as  well  as  new  ones  as  yet  undiscovered 
may  be  tried.  There  are  plenty  of  un found  materials 
which  may  be  much  better  than  those  now  in  use  and  a 
search  for  some  of  these  would  furnish  enough  excite- 
ment for  the  average  experimenter  for  some  little  time. 
It  is  well  to  remark,  however,  that  a  mere  duplication 
of  detectors  no  better  than  those  already  in  use  will  not 
be  of  much  importance  or  use.  What  is  wanted  is  some- 
thing better,  more  sensitive,  having  less  resistance,  and 
which  is  more  reliable  and  permanent. 

CONSTRUCTIONAL  DETAILS. 

There  are  a  great  variety  of  constructions  for  solid 
rectifying  detectors,  almost  every  experimenter  making  a 
different  kind  or  different  form.  Provided  that  the  fol- 
lowing general  requirements  are  adhered  to,  the  matter 
of  size,  adjustment  (mechanical  movement  used),  and 
form  is  of  little  consequence.  The  reader  has  unlimited 
latitude  and  opportunity  to  exercise  his  ingenuity.  A 
few  accepted  forms  which  are  similar  to  those  in  general 
use  and  favor  will  also  be  given. 

MATERIALS. 

The  crystals  in  general  use  can  be  had  from  supply 
houses.  Whenever  possible  tested  crystals  should  be 


Detectors.    Solid  Rectifiers. 


165 


purchased,  as  this  saves  considerable  time  and  trouble. 
For  instance,  it  may  happen  that  only  a  dozen  or  so  suit- 
able points  will  be  obtained  after  trying  out  a  pound  of 
material,  broken  up  into  points.  The  silicon  used  should 
be  fused  silicon,  the  carborundum  preferably  green  car- 
borundum, and  all  of  the  others  in  the  best  grade  obtain- 
able. Cheap  grades  generally  contain  considerable  for- 
eign matter  which  is  of  course  not  desirable.  Owing 
to  the  fact  that  the  most  commonly  used  crystals  are 
mentioned  in  the  claims  of  patents  held  practically  by 
one  holding  company,  many  dealers  in  minerals  and  crys- 
tals are  afraid  to  sell  them  for  fear  of  infringement 


PE. 


suits.  (See  chapter  19  on  the  experimenter's  rights). 
The  various  cups,  brass,  screws,  and  other  materials 
can  also  be  had  from  supply  houses. 

Crystal  mounting.  Fig.  54  shows  some  suitable  mount- 
ings for  the  crystals  to  form  the  large  contact  necessary. 
Two  spring  pieces  fastened  to  a  block  of  wood  as  at 
(a)  will  do.  Perhaps  the  best  mounting  is  that  shown 
in  the  figure  at  (b),  where  the  crystal  is  held  in  a  cup 
containing  a  fusible  alloy.  This  may  be  made  by  melt- 
ing four  parts  of  bismuth,  one  part  of  cadmium,  two 
parts  of  lead,  and  one  part  of  tin  together ;  or  three  parts 
of  a  good  grade  of  solder  instead  of  the  lead  and  tin, 


166  Experimental  Wireless  Stations. 

may  be  used.  The  melting  point  of  this  alloy  is  approxi- 
mately 138  degrees  F,  and  this  mixture  is  used  so  that 
the  resulting  heat  will  not  injure  the  crystal  as  ordinary 
solder  would.  The  cup  should  be  well  cleaned  before 
pouring  the  alloy  in,  and  around  the  crystal.  The  metal 
is  preferably  poured  into  the  cup  and  thtn  the  crystal 
is  placed  into  the  metal,  and  held  in  place  until  the  alloy 
cools.  A  substitute  for  this  method  is  to  pack  the  crystal 
in  the  cup  with  tinfoil  wads.  This  allows  the  crystal 
to  be  removed  so  that  the  sensitive  part  can  be  found. 
The  cap  from  a  round  dry  battery  carbon  can  be  used 
for  a  cup  if  it  is  well  cleaned  and  polished.  The  tinfoil 
can  be  packed  in  so  tight  that  the  crystal  will  not  fall 
out,  and  if  the  exposed  part  is  found  not  to  be  sensitive, 
the  crystal  can  be  removed,  turned  over,  and  tried  again, 
until  a  sensitive  part  is  found.  Many  similar  arrange- 
ments will  suggest  themselves  to  the  reader.  Almost  any 
form  of  spring,  clamp,  or  other  contact  which  will  make 
a  large  contact  and  hold  the  crystal  in  place  is  suitable. 
Use  the  crystal  as  follows. 

The  crystal  used  should  be  a  small  fragment  as  it 
will  then  work  as  well  or  better  than  a  large  piece.  It 
should  not  be  ground  and  should  be  left  in  its  natural 
shape.  Most  of  the  materials  are  best  used  as  small 
chunks.  Molybdenite  is  best  used  as  a  thin  sheet.  The 
molybdenite  may  be  easily  copper  plated  so  that  connected 
wires  can  be  directly  soldered  to  it.  When  a  pericon  set 
is  used,  the  zincite  should  have  a  larger  surface  than 
the  other  crystal.  The  latter  may  be  a  fragment  of  bornite 
or  chalcopyrite,  preferably  with  a  definite  point  for  con- 
tact. , 

In  making  a  universal  detector,  it  should  be  remem- 
bered that  three  types  of  contacts  will  be  needed  to  in- 
clude suitable  contacts  for  all  materials.  Crystals  like 


Detectors.    Solid  Rectifiers. 


167 


silicon  work  best  with  a  blunt  point  and  light  contact, 
molybdenite  with  a  blunt  point  and  comparatively  heavy 
contact,  those  like  galena  and  iron  pyrites  require  a  fine 
light  point,  and  those  like  carborundum  require  two  large 
contacts  with  a  comparatively  large  pressure.  An  ar- 


FIG. 55. 


FIG.5B. 


FIE. 57. 


rangement  which  will  provide  for  these  variable  condi- 
tions is,  therefore,  desirable.  Some  suitable  mechanical 
arrangements  are  shown  in  figs.  55 — 62.  In  the  clamp 
type,  the  crystal  can  be  removed  and  another  one  replaced, 


168 


Experimental  Wireless  Stations. 


while  in  the  multi-crystal  type  the  several  crystals  are 
mounted  so  that  any  one  may  be  used  at  a  time.  Where 
compactness  is  no  object  it  is  perhaps  a  better  plan  to 
have  a  plurality  of  separate  detector  stands  for  each  crys- 
tal. A  duplicate  detector  is  also  desirable,  so  that  when 
one  crystal  becames  poorly  adjusted,  another  sensitive  de- 
tector can  be  immediately  switched  into  circuit. 

Referring  to  the  figures,  which  were  collected  from 
various  sources,  figs  55,  56  and  57  show  suitable  con- 
structions for  a  simple  universal  detector  and  require  no 
further  comment.*  In  fig.  57,  A  represents  an  insulated 


FIC.5S. 


thumbscrew,  B  a  brass  spring  strip,  C  a  metal  standard 
of  round  or  square  brass,  D.  F.  G.  contacts  which  may 
be  used  for  a  variety  of  materials,  H  a  base,  I  a  brass 
strap,  and  J  a  notched  cup. 

Fig.  58  shows  another  universal  detector.  The  shaft 
A  slides  into  a  ball  B,  which  is  in  turn  held  by  the  str.DS 
Al  with  a  pressure  adjustable  by  F.  The  spring  S  keeps 
A  in  position.  C  is  a  simple  screw  chuck  holding  another 


*Pop.  Electricity.  Modern  Electrics.  U.  S.  Pat.  Speci- 
fication. 


Detectors.    Solid  Rectifiers. 


169 


chuck  D  in  which  a  point  is  in  turn  held.  Difficult  shaped 
points  may  be  used  in  this  manner.  The  crystal  is  held 
adjustably  in  a  clamp  A2.  The  arrangement  is  quite 
simple  and  allows  almost  any  desired  adjustment  and 
use. 

The  multi-cup  arrangement  of  fig.  59  is  taken  from 
patent  No.  1,  027,238,  U.  S.,  and  is  quite  simple.  The 
post  C  can  be  turned  so  that  the  contact  G.  makes  con- 


FIE. 53. 


FIG.  ED. 


FIC.G£. 


tact  with  any  one  of  the  cups  arranged  as  a  circle  on  the 
base.  The  contact  G  can  be  reversed  so  that  the  detector 
can  be  used  as  an  electrolytic  detector  with  one  of  the 
cups  K.  The  spring  I  provides  a  mild,  variable  pressure, 
and  the  rough  adjustment  is  made  by  the  screw  F  clamp- 
ing E  to  C  after  the  proper  length  has  been  found.  Fig. 
60  shows  a  simple  arrangement  suitable  for  galena,  iron 
pyrites  and  silicon,  and  needs  no  further  comment. 


170  Experimental  Wireless  Stations. 

Fig.  61  shows  a  delicate  adjustment  suitable  for  the 
small  movable  point  of  a  universal  detector.  Fig.  62 
shows  a  novel  scheme  for  adjusting  the  pressure  of  the 
small  point  on  the  crystal.  The  piece  B  is  mounted  on  a 
pivot  so  that  it  balances  nicely.  The  pressure  on  ths 
small  contact  can  then  be  varied  by  screwing  the  nut 
A  in  or  out,  thus  securing  more  or  less  weight  on  the 
fine  point. 

These  forms  are  only  reproduced  as  suggestions  as 
the  reader  can  easily  make  a  detector  according  to  his 
own  design.  Pericon  crystals  may  be  similarly  mounted, 
the  extra  crystal  replacing  the  fine  point. 

CARE  AND  ADJUSTMENT. 

Detectors  should  be  regarded  as  sensitive  and  deli- 
cate instruments.  They  should  be  kept  out  of  the  sunlight, 
away  from  dust  and  dirt,  acid  fumes,  and  similar  places. 

The  crystals  become  less  sensitive  after  a  time,  but 
can  often  be  renewed  by  cleaning  with  gasoline  or  carbon 
bisulphide,  using  an  old  tooth  brush  and  taking  great 
care  to  avoid  a  fire  or  even  a  burning  light,  because  both 
materials  and  particularly  the  bisulphide  are  very  explo- 
sive. Heat  alone  if  applied  rationally  will  often  restore 
an  old  crystal  to  sensitiveness  again. 

The  actual  adjustment  is  a  matter  which  must  be 
determined  by  experiment.  A  buzzer  test  is  very  valu- 
able for  this  purpose  and  should  be  a  part  of  every  wire- 
less receiving  set.  This  is  simply  a  common  buzzer,  such 
as  may  be  had  for  about  25  cents,  connected  to  a  key 
and  battery  and  to  a  short  aerial  wire  as  shown  in  fig 
63.  The  wire  need  only  be  a  few  feet  of  number  18  bell 
wire.  The  connections  can  be  arranged  on  the  aerial 
switch  so  that  when  the  switch  is  set  for  receiving, 


Detectors.    Solid  Rectifiers. 


171 


the  transmitting  key  will  operate  the  buzzer  instead  of 
the  transformer.  The  noise  of  the  buzzer  should  be 
deadened  by  covering  it  with  old  clothes  or  else  by  plac- 
ing the  buzzer  outside  of  the  building,  since  it  is  not  de- 
sirable to  hear  the  buzzing  sound.  This  buzzer  sets  up 
weak  wireless  waves  and  the  detector  is  in  adjustment 
when  the  said  waves  are  received  and  heard  the  loudest. 
Adjustment  of  the  detector  may  also  be  carried  out  while 


e 

02 

|l 

3 
D 

ijLJ        Short  Wire. 
B.lttr* 

f"* 

-ik 

PE. 

\ 

«*— 

hey 

FIG.G3. 

receiving  from  another  station,  provided  that  the  copy- 
ing of  the  message  is  of  secondary  importance  while  the 
adjustment  is  being  carried  out.  The  turning  on  and  off 
of  an  electric  light  socket  can  also  be  used  as  a  buzzer 
test,  the  resulting  arc  supplying  the  necessary  waves. 
While  we  are  on  this  subject  it  may  be  noted  that  a 
lamp  on  a  lighting  circuit  near  the  transmitting  station 
can  be  made  to  light  up  when  the  station  is  sending. 
Turn  the  lamp  on  and  then  unscrew  the  bulb  until  it 
just  goes  out.  The  transmitter  will  then  cause  it  to  light, 
when  the  key  is  pressed.  This  experiment  illustrates 
the  coherer  principle  to  a  certain  extent  and  will  only 
work  when  the  light  is  in  close  proximity  to  the  trans- 
mitter. 


CHAPTER  XF. 


TELEPHONE  RECEIVERS.  —  DETECTORS   FOR 

CONTINUOUS  WAVES.  —  EINTHOVEN 

GALVANOMETER. 

In  order  to  receive  from  a  continuous  wave  transmit- 
ter such  as  a  telegraph  transmitter  operated  by  an  arc 
generator  or  quenched  arc  generator,  which  is  not  audibly 
altered  at  the  transmitter,  it  is  necessary  to  modify  the 
received  impulses  audibly  at  the  receiver.  The  human  ear 
can  only  hear  or  recognize  vibrations  whi^h  do  not  ex- 
ceed 35,000  or  40,000  per  second,  so  that  the  waves  sent 
out  from  an  arc  generator  vibrating  at  many  times  this 
rate  are  inaudible.  The  only  form  of  indicator  which 
will  efficiently  record  such  inaudible  waves  without  modi- 
fying them  at  the  receiver  by  a  vibrator  or  chopper  is  the 
Einthoven  galvanometer,  as  far  as  the  author  is  aware. 
While  this  is  a  delicate  instrument,  a  brief  account  of 
it  will  be  given  so  that  it  may  be  constructed  by  skilled 
workers. 

EINTHOVEN  GALVANOMETER. 

This  instrument  consists  essentially  of  a  fine  wire 
stretched  between  the  pole  pieces  of  a  powerful  electro- 
magnet. This  wire  may  be  of  platinum,  silver,  aluminum, 
or  copper,  and  should  be  very  fine.  No.  40  or  50  such  as 
is  used  for  telephone  receivers  can  be  used.  The  con- 
struction and  arrangement  is  shown  in  fig.  64.  In  the 


Sensitive  Indicators  for  Receiver. 


173 


most  sensitive  forms,  a  thin  quartz  or  glass  fibre  which 
has  been  platinized  is  used  and  if  this  can  be  had  from 
a  supply  house,  the  reader  is  advised  to  purchase  it.  The 
fine  wire  is  mounted  on  T  shaped  set  screws  C  and  F, 
so  that  the  tension  can  be  delicately  adjusted.  As  shown, 
this  is  accomplished  by  having  C  attached  to  a  rod  having 
a  cam  K  on  its  upper  end  and  held  in  place  by  a  spring 
L.  When  the  lever  Kl  presses  down  on  the  rod,  a  very 


FIG.E4-. 


fine  adjustment  is  secured.  Kl  is  operated  by  a  micro- 
meter screw  J,  as  shown.  A  more  simple  arrangement 
would  also  do,  but  the  adjustment  would  then  be  less 
accurate,  and  more  difficult  to  carry  out. 

The  smaller  part  of  the  figure  shows  the  position  of 
the  wire  and  magnets  and  one  method  for  observing  the 
displacement  of  the  wire.  The  eye  piece  AE  is  inserted 


174  Experimental  Wireless  Stations. 

in  a  hole  in  one  of  the  magnet  poles.*  Light  is  pro- 
jected by  the  tube  C  and  lens  F.  When  the  current  flows 
in  the  direction  of  the  arrows,  the  wire  stretched  between 
CC  has  a  deflection  indicated  by  the  arrow  a.  This  dis- 
placement can  be  magnified  by  projection  upon  a  screen, 
in  which  case  the  eye  piece  is  removed  and  a  strong 
light  applied  at  C.  This  recorder  is  very  sensitive  and 
can  be  used  for  long  distance  work  as  well  as  for  ex- 
perimental measurements.  The  amount  of  deflection  in- 
dicates the  strength  of  the  received  signal.  In  practice, 
a  photographic  record  is  taken  by  means  of  a  moving  film, 
so  that  a  permanent  record  of  the  message  as  a  defined 
line  according  to  the  dots  and  dashes,  is  the  result.  The 
experimenter  may  dispense  with  the  photographic  record, 
however.  The  skilled  reader  should  not  find  it  difficult 
to  make  a  duplicate  from  this  brief  description.  The 
magnet  used  should  consume  about  250  to  500  watts,  and 
it  is  not  unlikely  that  ready  wound  magnet  coils  can  be 
pressed  into  service  for  experimental  purposes.  The  suc- 
cess of  the  instrument  depends  on  the  fact  that  the  fine 
wire  has  a  rapid  period.  The  instrument  will  not  be  of 
any  use,  however,  unless  delicately  constructed. 

In  order  to  receive  unaltered  continuous  waves  with 
an  ordinary  wireless  telephone  head  receiver,  the  received 
impulses  must  be  modified,  interrupted  or  chopped.  This 
can  be  done  by  the  arrangement  of  fig.  65,  in  which  the 
relay  shown  is  a  20  ohm  or  75  ohm  telegraph  relay,  hav- 
ing its  magnet  connected  to  an  alternating  current  line 
through  a  lamp.  The  secondary  platinum  terminals  are 
used  to  alternately  connect  and  disconnect  a  large  fixed 
condenser  in  the  receiving  circuit  as  shown,  thus  balancing 
and  unbalancing  the  circuit  at  an  audible  frequency  so 

*  Old  microscope  parts  can  be  used. 


Sensitive  Indicators  for  Receiver. 


175 


that  the  received  signals  are  rendered  audible.  Thh  ar- 
rangement also  effectually  cuts  out  a  great  deal  of  other 
interference.  When  ordinary  stations  are  to  be  heard  the 
relay  is  merely  disconnected  from  the  line.  The  re- 
mainder of  the  circuit  is  familiar  or  will  soon  be  and 
needs  no  further  comment.  The  relay  acts  as  an  inter- 
rupter and  may  be  used  to  throw  either  capacity  or  in- 
ductance or  both  in  and  out  of  the  circuit.  The  insert 
shows  a  simple  method  for  the  same  purpose.  In  this 
case  a  single  condenser  is  used  in  shunt  about  the  tele- 


phone  receivers.     The  remainder  of  the  circuit  is  not 
shown  as  it  is  the  same  as  before. 

Either  the  Einthoven  galvanometer  or  this  chopper 
arrangement  will  be  satisfactory  to  detect  the  continuous 
waves.  With  this  arrangement,  experimenters  may  re- 
ceive from  the  Poulsen  stations  provided  that  the  cir- 
cuits are  properly  tuned.  In  connection  with  the  ap- 
paratus described  in  chapter  12  for  telegraphy  without 
modifying  the  continuous  waves  at  an  audible  frequency 
at  the  transmitter,  this  form  of  detector  forms  an  ideal 
one  for  the  experimenter.  A  somewhat  similar  arrange- 
ment is  sometimes  incorporated  directly  in  the  detector, 
but  since  it  is  less  efficient,  it  will  not  be  described  here. 


176  Experimental  Wireless  Stations. 

The  continuous  wave  system  with  a  chopper  at  the  re- 
ceiving station  is  perhaps  the  most  advanced  system  in 
the  art  at  the  present  writing,  and  without  a  chopper, 
using  the  galvanometer,  the  messages  can  be  permanently 
recorded  as  fast  as  they  are  sent.  Sharper  tuning  is 
also  possible  and  good  transmission  is  possible  on  ac- 
count of  the  accumulative  effect  at  the  receiving  station. 

If  carefully  constructed  the  galvanometer  described 
will  respond  to  a  sufficient  extent  when  operated  by  only 
.0001  volt. 

TELEPHONE  RECEIVERS. 

Ordinary  telephone  receivers  may  be  used  as  recorders 
for  experimental  work  over  short  distances,  but  specially 
constructed  wireless  receivers  are  necessary  when  long 
distance  work  is  to  be  done.  The  receivers  in  general 
use  are  of  the  watch  case  type  and  either  one  or  two 
receivers  on  a  headband  may  be  used.  Since  most  people 
are  able  to  hear  much  better  with  one  ear  than  the  other, 
it  is  an  advantage  to  use  only  one  receiver  on  the  head- 
band and  to  block  off  the  other  ear  from  foreign  sounds 
by  a  rubber  pad.  This  method  is  less  expensive  than 
when  two  receivers  are  used  on  a  headband.  However, 
if  two  receivers  are  used  they  must  be  identical  in  their 
dimensions  and  windings  as  otherwise  the  one  having  the 
least  resistance  or  other  unequal  dimension  will  not  work 
in  accordance  with  the  other  one.  Many  manufacturers 
are  now  making  reliable  light  weight  receivers  suitable  for 
the  most  exacting  wireless  work,  and  while  the  latter  are 
perhaps  a  little  expensive,  they  are  essential  to  efficient 
work,  particularly  over  long  distances.  The  reason  why 
a  low  resistance  telephone  receiver  such  as  is  used  for 
telephone  work  is  not  suited  for  delicate  wireless  work 


Sensitive  Indicators  for  Receiver.  177 

is  that  it  is  made  to  give  a  loud  response  with  a  com 
paratively  large  amount  of  applied  energy  but  will  not 
give  any  response  with  very  minute  currents,  such  as  are 
produced  by  a  detector  receiving  from  a  distant  statior. 
An  ordinary  receiver  can  be  rewound,  however,  with 
No.  40  or  50  enameled  wire  so  that  its  utility  will  be 
much  greater.  When  this  is  done  a  new  and  thinner 
diaphram  should  also  be  supplied,  since  the  ordinary 
diaphram  is  too  thick  for  wireless  purposes.  These  thin 
diaphrams  may  be  had  at  supply  houses  and  are  known 
as  gold  diaphrams  because  they  are  gold  plated.  A  wire- 
less receiver  is  not  intended  to  give  a  loud  response,  but 
rather  to  give  an  audible  and  working  response  with  very 
feeble  currents.  The  resistance,  however,  is  not  the 
real  delicate  part  of  the  receiver,  and  the  mere  state- 
ment that  a  receiver  is  wound  to  1,500  ohms  means 
little  or  nothing.  What  is  desired  is  a  large  number  cf 
ampere  turns,  and  since  this  is  best  secured  by  usin? 
fine  copper  wire,  No.  38  or  40  is  generally  employed. 
Receivers  are  rated  according  to  their  resistance  largel/ 
because  this  is  a  convenient  measure,  but  as  far  as  work- 
ability is  concerned,  the  number  of  ampere  turns  is  the 
essential  factor  which  determines  the  actual  utility.  In 
any  case,  a  resistance  of  over  1,500  ohms  is  no  advar- 
tage,  and  a  resistance  of  less  than  800  ohms  is  net 
desirable  when  the  receivers  are  to  be  used  with  solid 
rectifying  detectors. 

CARE  AND  ADJUSTMENT. 

While  a  receiver  seldom  requires  attention  after  it 
has  been  adjusted,  it  should  be  kept  clean,  and  free  from 
dust  and  moisture.  When  rewound  receivers  are  used 
it  is  sometimes  necessary  to  adjust  the  distance  of  the 


178  Experimental  Wireless  Stations. 

diaphram  from  the  poles.  This  can  be  done  by  using 
a  soft  rubber  cushion  between  the  cap  and  the  receiver 
case,  and  screwing  the  cap  on  with  more  or  less  pressure, 
thus  adjusting  the  distance  between  the  diaphram  and 
the  receiver's  magnet  pole.  After  long  use,  the  perma- 
nent magnets  should  be  tested  and  if  the  magnetic  at- 
traction is  weak,  the  magnet  should  be  strengthenei  by 
remagnetization.  A  common  test  is  to  judge  by  the  dis- 
tance between  the  receiver  case  and  diaphram,  which  is 
necessary  just  before  the  diaphram  (previously  removed 
and  laid  on  a  table),  is  attracted  to  it. 

Receivers  are  seldom  burnt  out.  This  may  be  th<* 
case  after  a  station  has  been  subjected  to  a  heavy  static 
or  lightning  discharge.  The  headband  used  should  be 
comfortable  and  should  keep  the  receiver  tight  against 
the  ear.  The  receiver  is  very  important  and  its  sensi- 
tiveness together  with  the  hearing  ability  of  the  operator 
is  one  of  the  largest  factors  which  determine  the  receiving 
range  of  a  station. 

A  word  concerning  standard  receivers  for  wireless 
purposes.  The  magnets  should  be  permanent  and  prefer- 
ably of  the  consequent  pole  type,  to  prevent  leakage  about 
the  pole  pieces.  The  diaphram  should  be  thin  and  uni- 
form, but  of  sufficient  thickness  to  absorb  sufficient  mag- 
netic flux.  The  poles,  case,  and  diaphram  should  be  pro- 
portioned and  made  so  that  the  maximum  sensitiveness 
and  least  liability  to  injury  and  change  is  the  result. 
Lightness  and  a  good  fit  are  important  items  as  far  as 
comfort  is  concerned,  and  if  the  receivers  are  to  be  used 
continually,  this  is  a  very  important  consideration.  A 
suitable  size  for  the  wire  used  in  the  coils  is  No.  40  or 
wire  .0031  thick.  A  standard  thickness  for  the  diaphram 
is  .004  thick  exclusive  of  the  plate  or  varnish  coat,  which 
last  is  to  prevent  rust  and  corrosion. 


Sensitive  Indicators  for  Receiver.  179 

HOW  THE  RECEIVER  OPERATES. 

It  is  well  known  to  the  readers  that  the  telephone 
receiver  depends  upon  simple  magnetic  phenomena,  so 
an  account  of  the  action  will  be  dispensed  with.  How- 
ever, it  is  well  to  understand  the  action  in  a  wireless 
receiving  set. 

We  have  seen  that  the  detector  rectifies  the  oscilla- 
tory current  into  a  pulsating  direct  current.  Now,  this 
direct  current  passes  through  the  windings  of  the  re- 
ceiver and  causes  the  diaphram  to  be  pulled  according 
to  the  strength  and  changes  in  the  current.  While  the 
current  supplied  to  the  telephone  may  have  as  much 
as  a  million  pulsations  in  one  second,  the  ear  only  hears 
a  sound  similar  to  that  produced  by  a  steady  current 
on  account  of  the  regulation  exerted  by  the  inductance 
of  the  windings  of  the  receiver.  That  is,  each  complete 
wave  train  after  being  rectified  by  the  detector  causes 
only  one  pull  on  the  diaphram,  so  that  the  operator  hears 
one  sound  corresponding  to  each  transmitted  wave  train. 
However,  a  complete  signal,  even  a  dot,  generally  com- 
prises several  successive  wave  trains  so  that  the  received 
signal  is  heard  as  a  succession  of  clicks  corresponding 
to  the  spark  rate  and  speed  at  which  the  message  is  sent. 
The  receiver  gets  the  message  almost  the  same  moment 
that  it  is  sent,  since  the  waves  travel  at  the  rate  of  186,000 
miles  per  second,  and  the  frequency  tone,  wave  length 
and  other  variable  factors  are  practically  the  same  as 
when  the  impulses  leave  the  transmitting  aerial. 


180 


Experimental  Wireless  Stations. 


MEASURING  THE  INTENSITY  OF  THE 
SIGNAL.* 

For  experimental  work  it  is  often  desirable  to  com- 
pare the  relai'.ve  strengths  of  the  signals  received  either 
from  two  stat;ons  or  from  the  same  station  using  differ- 
ent instruments  or  circuits.  A  suitable  simple  arrange- 
ment for  this  purpose  is  shown  in  figure  66,  and  consists 
simply  of  a  calibrated  shunt  resistance  about  the  phones. 
A  non-inductive  resistance  box  is  suitable.  The  value 
of  the  received  current  in  the  telephone  receiver  is  prac- 
tically proportional  to  the  energy  of  the  incoming  waves 
so  that  a  roue'li  table  of  values  based  on  audibility  is  easily 


—  G. 


made.  Thus  a  station  which  produces  a  sound  just  aud- 
ible in  the  receivers  when  all  the  resistance  is  in  circuit 
may  be  taken  ac  a  standard.  If  another  station  just  pro- 
duces an  audible  sound  when  one-half  of  the  total  resis- 
tance is  in  circuit;  the  new  value  can  be  compared  with  the 
standard.  The  calibration  could  just  as  well  be  the  other 
way  around  so  that  the  standard  is  audibility  with  no 
shunt  resistance.  The  result  is  best  expressed  as  a  frac- 
tion of  or  so  many  times  audibility,  as  the  case  may  be. 

*  This  method  can  also  be  used  to  eliminate  interfer- 
ence from  weak  stations,  but  is  carried  out  at  the  expense 
of  a  decrease  in  the  intensity  of  the  received  signal.  It 
can,  however,  be  utilized  in  connection  with  a  wave 
meter. 


CHAPTER  XVI. 


TUNING— INTERFERENCE  PREVENTION. 

If  the  reader  will  bear  in  mind  the  discussions  given 
for  resonant  circuits  at  the  transmitting  station,  the  re- 
quirements for  tuning  at  the  receiving  station  will  not 
be  difficult  to  understand.  The  two  circuits  are  in  fact 
quite  similar  in  some  respects.  The  detector  corresponds 
to  the  spark  gap  and  as  the  transmitter,  this  detector 
constitutes  one  of  the  greatest  factors  of  resistance  in 
the  circuit.  As  in  the  case  of  the  spark  gap  this  resist- 
ance damps  the  oscillations  and  makes  sharp  tuning  diffi- 
cult. The  resistance  of  the  detector,  then,  prevents  ab- 
solute tuning.  As  far  as  the  rest  of  the  apparatus  and 
circuits  are  concerned,  absolute  tuning  can  be  very  nearly 
reached  if  desired.  Now,  the  tuning  apparatus  and  cir- 
cuit to  employ -for  experimental  purposes  will  vary  with 
the  local  conditions.  In  cities  like  New  York,  where 
the  interference  is  considerable,  very  sharp  tuning  is  de- 
sirable at  both  the  transmitter  and  receiver,  while  in  lo- 
calities where  there  are  only  a  few  scattered  stations, 
simple  circuits  with  rough  tuning  will  suffice,  so  that  the 
intensity  of  the  signal  is  about  all  that  needs  attention. 
In  most  of  the  present  tuning  methods,  fine  tuning  is 
carried  out  at  the  expense  of  the  intensity  of  the  received 
signal,  but  for  practical  purposes  all  that  is  needed  is  a 
distinct  audible  signal.  Close  tuning  has  one  disadvantage 
in  that  a  message  can  easily  be  missed  if  the  apparatus 


182  Experimental  Wireless  Stations. 

is  at  the  wrong  adjustment.  In  arranging  a  receiving 
set  it  is  well  to  bear  in  mind  the  use  to  which  the  appa- 
ratus is  to  be  put  and  to  provide  for  the  design  accor- 
dingly. An  ideal  set,  in  the  author's  opinion,  is  one  which 
provides  two  standby  points  and  a  variable  close  tuning 
or  interference  arrangement.  One  of  the  standby  adjust- 
ments is  for  the  standard  200  meter  experimental  wave 
length  and  the  other  standby  adjustment  is  for  the  stand- 
ard 300  meter  commercial  wave  length.  After  the  mess- 
age has  started,  any  interference  which  may  arise  or  be 
in  progress  can  then  be  tuned  out  or  dissipated  by  the 
sharp  tuning  adjustments.  There  are  several  arrange- 
ments which  will  give  this  ideal  outfit  and  the  several 
parts  will  be  described  in  some  detail  later.  For  the 
present,  a  close  attention  to  the  theory  and  design  is  of 
the  first  importance. 

In  localities  where  there  is  little  or  no  interference, 
elaborate  receiving  apparatus  is  not  necessary  or  even 
desirable.  Aside  from  the  extra  expense,  the  compli- 
cated receiving  circuits  involve  greater  skill  and  require 
more  experience  to  operate.  Experimenters  should  spend 
much  more  time  in  tuning  the  transmitter  than  in  tuning 
the  receiver,  in  most  cases,  as  the  former  is  really  more 
important  and  instructive.  The  item  of  interference  will 
be  taken  up  first. 

INTERFERENCE. 

If  there  was  no  interference  in  wireless  work,  all  that 
would  be  necessary  at  the  receiving  station  is  a  simple 
inductance  with  which  to  alter  the  receiving  wave  length 
so  that  the  receiver  can  be  brought  into  resonance  with 
the  transmitter.  As  it  happens,  however,  the  average 
station  must  be  designed  to  work  through  both  natural 


Tuning — Interference  Prevention.  183 

and  artificial  interferences.  It  may  be  explained  that  the 
term  "interference"  includes  all  foreign  disturbances 
which  impede  or  interfere  with  the  regular  reception  of 
a  desired  message. 

NATURAL  INTERFERENCE. 

Mechanical  vibrations,  waves  received  from  street  arc 
lights,  induction  from  power  and  telephone  lines,  static 
and  similar  disturbances  are  natural  causes  of  inter- 
ference and  can  be  overcome  in  nearly  every  case  by  the 
use  of  proper  shunt  circuits.  A  looped  aerial  is  best  to 
adopt  when  these  disturbances  are  particularly  marked. 
With  the  exception  of  strong  static  disturbances,  these 
natural  disturbances  can  be  controlled  and  either  dissi- 
pated or  neutralized.  Ordinary  static  disturbances  result 
from  the  discharge  of  static  electricity  which  accumulates 
on  the  aerial.  This  form  of  disturbance  is  particularly 
marked  during  the  summer  months  and  is  very  annoying. 
It  can  only  be  dissipated  when  not  too  strong  and  then, 
at  the  expense  of  the  loss  of  intensity  of  the  received 
signal.  During  electrical  storms  receiving  becomes  quite 
dangerous  and  impracticable.  Experimenters  are  advised 
to  abandon  the  use  of  the  aerial  during  local  electrical 
storms.  Although  the  use  of  short  aerials  of  low  height 
does  not  ordinarily  mean  a  liability  to  much  danger,  it 
is  well  to  be  on  the  safe  side.  Mechanical  vibrations 
can  be  taken  up  by  using  cloth  or  rubber  pads  on  the 
instruments. 

ARTIFICIAL  INTERFERENCE. 

This  is  the  form  of  interference  resulting  from  reg- 
ular wireless  communication  between  several  stations 
within  the  range  of  each  other.  The  manner  of  over- 


184  Experimental  Wireless  Stations. 

coming  this  to  a  large  extent,  by  the  use  of  resonant 
transmitters  having  definite  wave  lengths,  has  already 
been  pointed  out  in  detail.  If  every  station  (this  means 
both  commercial  and  experimental)  would  use  just 
enough  power  to  transmit  to  the  desired  station,  sharply 
tuned  resonant  circuits,  a  definite  wave  length  and  "wire- 
less sense,"  the  difficulty  of  the  problem,  even  with  simple 
instruments  of  the  present  design,  would  be  much  re- 
duced. In  its  average  or  worst  form,  artificial  interfer- 
ence means  working  through  from  four  to  a  dozen  or 
more  other  stations,  simultaneously  sending  at  approxi- 
mately the  same  band  of  wave  lengths  and  same  intensity. 
The  operator  who  receives,  however,  cannot  regulate  the 
coupling  or  adjustments  of  the  several  transmitting  sta- 
tions and  must  accept  conditions  as  they  exist.  The  sev- 
eral items  must  be  successfully  met  and  the  interference 
dissipated  without  losing  the  desired  message.  While  this 
is  not  always  possible,  it  can  generally  be  approximated. 
The  worst  item  to  overcome  is  the  matter  of  forced  waves, 
or  those  which  seems  to  come  in  at  every  wave  length  on 
account  of  the  proximity  and  heavy  coupling  of  the  trans- 
mitter. When  the  interference  prevention  methods  to  be 
described  are  employed,  these  forced  wave  disturbances 
can  be  practically  eliminated  in  nearly  every  case.  While 
the  use  of  limited  or  restricted  waves  will  prevent  inter- 
ference between  commercial  and  experimental  stations, 
the  experimenters  must  still  fight  it  out  among  themselves. 
In  some  respects  the  difficulty  will  be  even  more  marked 
since  short  wave  lengths  are  less  immune  from  inter- 
ference than  the  long  wave  lengths.  However,  the  ex- 
perimenter may  receive  from  any  and  every  station  within 
range  without  difficulty,  if  the  simple  relations  of  a  tuned 
receiving  set  are  understood. 


Tuning — Interference  Prevention.  185 

TUNING  METHODS. 

It  must  be  remembered  that  the  ordinary  station  emits 
at  least  two  defined  wave  lengths.  The  sharper  the  two 
are  defined,  the  better  as  far  as  the  receiving  operator 
is  concerned.*  With  quenched  spark  or  arc  stations 
sharply  tuned,  practically  a  single  sharp  wave  length  is 
all  that  needs  to  be  considered,  but  interference  from 
other  stations  operating  at  the  same  wave  length  often 
complicates  the  matter.  It  may  be  stated  right  now  that 
the  number  of  possible  connections  for  the  receiving  cir- 
cuit is  practically  unlimited,  but  that  many  so  called  hook- 
ups are  a  mere  duplication  or  fresh  dressed  forms  for  old 
circuits  and  really  accomplish  nothing.  In  building  and 
arranging  the  apparatus  for  the  receiving  circuit,  the 
actual  factors  concerned  and  the  remedies  should  receive 
attention  rather  than  a  hit  and  miss  elaboration  of  the 
circuits  without  conforming  to  the  requirements.  Bear- 
ing in  mind  that  tuning  the  receiver  means  nothing  more 
or  less  than  altering  the  circuits  by  adjusting  the  amount 
of  capacity  and  inductance  used,  (resistance  is  also  a 
factor),  the  following  summary  will  aid  in  designing  a 
receiver. 

FACTORS  AND  REQUIREMENTS  FOR  TUNING 
THE  RECEIVER. 

1.  Close  coupling  at  the  receiver  should  be  used  when 
the  transmitter  is  close  coupled  and  vice  versa. 

2.  With  the  receiver  tuned  to  the  desired  transmitter, 
a  large  amount  of  the  disturbance  can  be  eliminated  by 
reducing  the  coupling,  until  the  strength  of  the  signals 
is  just  distinct. 

3.  A  shunt  resistance  as  described  in  chapter  15  may 
be  used  as  a  substitute  for  or  in  addition  to  method  2. 

*  See  diagrams  in  Chapter  4. 


186  Experimental  Wireless  Stations. 

4.  The  two  wave  lengths  sent  by  a  transmitter  being 
designated  as  short  and  long,  tuning  for  either  the  long  or 
the  short  wave  (Detuning)  to  an  extreme  degree  is  often 
a  marked  advantage.     Since  the  short  wave  is  generally 
the  least  desirable,  the  aerial,  circuit  of  the  receiver  is 
best  thrown  out  of  tune  on  the  short  wave  side  as  much 
as  is  possible. 

5.  When  the  desired  message  comes  in  quite  loud, 
the  insertion  of  some  resistance  directly  in  the  aerial  cir- 
cuit will  often  cut  out  disturbances,  but  at  the  expense  of 
the  intensity  of  the  signal. 

6.  -In  tuning,  remember,  that  an  inductance  in  series 
with  the  aerial  or  a  capacity  in  shunt  with  a  series  in- 
ductance in  the  aerial  circuit,  increases  the  receiving  wave 
length.    A  series  capacity  in  the  aerial  circuit  on  the 
other  hand,  decreases  the  receiving  wave  length. 

7.  A  closed  or  looped  aerial  will  eliminate  most  of 
the  natural  disturbances. 

8.  The  disturbing  impulses  can  be  made  to  oppose 
and  neutralize  each  other,  while  the  desired  signal,  (at 
a  reduced  intensity),  is  received.     (Differential  method). 
(Bridge  method).     This  is  a  very  desirable  method,  and 
if  the  waves  are  in  a  sufficiently  long  train,  it  is  possible 
to  discriminate  between  them  and  undesired  impulses. 
If  the  undesired  impulses  are  more  rapidly  damped  than 
the  desired  impulses  they  can  be  avoided,  even  when  they 
are  of  the  same  period  as  the  desired  waves,  under  favor- 
able conditions. 

We  shall  now  discuss  approved  circuits  embodying 
the  above  principles,  starting  with  the  more  simple  ones. 
As  has  already  been  stated  these  may  be  varied  almost 
at  will,  the  essential  forms  being  given  wherever  prac- 
ticable. While  a  brief  outline  of  the  operation  will  be 
given,  a  close  study  of  the  diagrams  will  be  necessary  in 


Tuning — Interference  Prevention. 


187 


at  least  part  of  the  cases.    The  numbers  which  follow 
do  not  correspond  with  the  numbers  for  the  foregoing 


«M#4l 


-J    0 


PI 

N 

M«E2irE 


^c    j  rrr»nfif»s  w  ^j 

^P/f«*°= 

LLli 


summary. 

1.    Fig.  67.     Simple  tuned  circuit  with  wave  length 


188  Experimental  Wireless  Stations. 

varied  by  adding  more  or  less  inductance  to  the  antenna. 
The  particular  inductance  indicated  is  known  as  a  single 
slide  tuner.  The  condenser  in  shunt  about  the  detector 
increases  the  intensity  of  the  received  signal.  While 
desirable,  it  may  be  dispensed  with  for  short  distance 
receiving.  The  coupling  is  fixed  in  this  arrangement  and 
while  it  is  useful  to  bring  a  station  to  approximate  reso- 
nance with  the  transmitter,  close  tuning  or  prevention 
of  interference  is  not  possible.  In  this  and  other  dia- 
grams the  letter  A  denotes  the  aerial,  G  the  ground,  D 
the  detector,  C  a  fixed  condenser,  and  T  the  receivers. 
L.  represents  the  inductance. 

2.  Fig.  68.     Same  as  before,  except  that  a  shunt 
variable  condenser  VC  is  provided.     An  increase  of  ca- 
pacity of  VC  increases  the  wave  length. 

3.  Fig.  69.     Double  slide  tuner.     Coupling  of  the 
circuit  can  be  changed,  but  must  be  relatively  close.     De- 
sirable where  little  interference  is  met  with. 

4.  Fig.  70.     Three  slide  tuner.     Same  as  before,  ex- 
cept that  the  coupling  of  the  aerial  and  detector  circuit 
can  be  varied  to  a  larger  extent.     The  position  of  the 
two  circuits  can  be  varied.     Thus  with  the  sliders  in- 
cluding the  detector  circuit  remaining  a  uniform  distance 
apart,  they  can  both  be  shifted  up  or  down  the  turns  of 
wire,  while  the  ground  slider  remains  fixed  or  also  be- 
comes changed.     The  relative  positions  of  the  aerial  and 
detector  circuits  can  thus  be  changed.     The  desired  ad- 
justment can  only  be  found  by  trial  and  when  once  found 
should  be  noted  before  changes  are  made. 

5.  Fig.  71.     Bridge.     Three  slide  tuner  with  the  de- 
tector circuit  shunted  around  the  terminals  of  the  wire. 
Four  or  five  slides  would  be  better  to  use.     When  both 
branches  of  the  divided  circuit  are  maintained  in  a  sym- 
metrical  condition   the    received   impulses   are   equally 


Tuning — Interference  Prevention.  189 

divided  so  that  they  have  no  effect  on  the  detector.  The 
arrangement  is  like  a  Wheatstone  bridge,  the  detector 
corresponding  to  the  galvanometer,  and  was  devised  by 
S.  G.  Brown.  Now,  to  receive  the  desired  signals,  the 
ground  contact  is  shifted  to  the  right  or  left  until  the 
best  position  for  the  desired  impulses  is  found.  (See 
8  of  the  foregoing  summary.) 

6.  Fig.  72.  Loose  coupler,  LC.  Sharp  tuning  is 
possible  because  the  coupling  can  be  greatly  varied.  This 
is  a  very  popular  form  of  tuner,  and  while  it  derives  its 
name  from  the  fact  that  the  secondary  can  be  pulled 
away  from  the  primary,  the  heaviest  coupling  is  reached 
when  the  middle  of  the  active  primary  turns  is  directly 
over  the  middle  of  the  active  secondary  turns.  When  the 
sliding  secondary  is  inserted  farther  in  the  primary  after 
this  point  has  been  reached,  the  coupling  again  becomes 
loose.  Since  this  form  is  best  adopted  as  a  standard  be- 
cause of  its  utility  and  comparative  simplicity,  its  relations 
and  pecularities  will  be  more  fully  described.  The  fol- 
lowing abridgement  from  an  article  in  Popular  Electricity 
by  M.  O.  Andrews  is  of  interest  in  this  connection. 

"1.  Increasing  the  inductance  of  the  primary  increases  the 
long-  wave  length  rapidly,  but  the  short  wave  length  is  increased 
so  slowly  that  it  may  be  considered  as  remaining  constant.  The 
opposite  is,  of  course,  true  when  inductance  is  taken  from  the 
primary. 

2.  Increasing  the  inductance  of  the  secondary  increases  both 
the  long  and  the  short  wave  lengths  equally,  or  nearly  so,  and 
vice  versa. 

3.  Loosening  the  coupling  between  the  primary  and  second- 
ary  decreases   the   long   wave   length   and   increases   the    short 
wave  length.     Tightening  the  coupling  increases  the  long  and 
decreases  the  short  wave  lengths.     In  other  words,  its  action  is 
the  same  as  the  oscillation  transformer  of  the  transmitting  set. 
As  the  coupling  is  loosened  the  two  wave  lengths  approach  the 
wave  length  to  which  each  circuit  is  individually  tuned,  and  as 
the  coupling  is  closed  the  two  wave  lengths  are  driven  farther 
from  the  natural  wave  length  of  the  circuits. 

4.  Increasing  the  capacity  in  the  primary  circuit  increases 
both  wave  lengths,  and  vice  versa. 


190  Experimental  Wireless  Stations. 

6.  The  variable  capacity  in  the  secondary  circuit  is  used 
principally  to  put  the  secondary  in  resonance  with  the  primary, 
thereby  allowing  looser  coupling:  than  would  otherwise  be  pos- 
sible. This  allows  atmospheric  disturbances  to  be  cut  out  to 
some  extent  without  decreasing  the  audibility  of  the  signals. 

We  have  already  observed  that  it  is  possible  to  hear  a  station 
radiating  a  double  wave  at  two  places  on  our  tuner.  In  one 
case,  we  are  in  tune  with  the  long  wave  and  in  the  other  with 
the  short  wave.  We  may  also  be  in  tune  with  both  the  long  and 
the  short  waves  at  the  same  time.  This  is  a  decided  advantage, 
as  we  will  then  receive  energy  from  both  waves,  and  the  signals 
will  consequently  be  much  louder  than  when  tuned  to  only  one 
of  the  waves. 

How  may  the  different  types  of  interference  be  avoided? 

Case  1.  When  in  tune  with  the  long  wave  length  of  the 
transmitting  station,  there  are  four  principle  types  of  interfer- 
ence that  we  must  dodge. 

1.  Another  station  may  commence  sending,  whose  long  wave 
is  of  the  same  length  as  the  one  which  we  are  receiving,  but 
whose  short  wave  is  either  longer  or  shorter  than  the  short 
wave  of  the  station  from  which  we  are  receiving.     For  instance, 
suppose   we  are  receiving  from  a  station  radiating  waves  of 
1,500  and  500  meters  respectively.     We  are  tuned  to  1,500  and 
400  meters,  and  another  station  commences  sending  using  waves 
of  1,500  and  600  meters.     By  referring  to  the  effects  of  coupling 
on  double  waves  we  find  that  this  type  of  interference  may  be 
tuned  out  by  simply  loosening  the  coupling  which  lowers  our 
long  wave  length  perhaps  to  1,300  meters  and  raises  our  short 
wave  length  to  500  meters.     The  desired  signals  will  then  come 
in  not  on  the  long  wave,  but  on  the  short  wave,  where  there  is 
no  interference.     If  the  coupling  is  loosened  too  much  our  short 
wave  length  will  be  raised  to  600  meters,  where  the  undesired 
signals  will  again  be  picked  up. 

2.  While  we  are  still  tuned  to  1,500  and  400  meters,  and  are 
receiving  from  a  station  radiating  waves  of  1,500  and  500  me- 
ters, another  station  may  begin  sending,  using  a  short  wave  of 
400  meters  and  a  long  wave,  either  longer  or  shorter  than  1,500 
meters.     It  may  be  tuned  out  by  adding  capacity  to  the  primary 
circuit,   which   increases   both   wave   lengths   to   1,700   and    600 
meters,  then  by  loosening  the  coupling  our  long  wave  length  is 
again  brought  back  to  1,500  meters  and  our  short  wave  length 
driven  still  farther  from  the  interference  at  400  meters.     The 
desired  signals  will  again  come  in  on  the  long  wave,  but  our 
short  wave  length  has  been  raised  to  800  meters,  where  it  is 
comparatively  safe  from  interference,  as  there  are  very  few  sta- 
tions using  wave  lengths  of  from  600  to  900  meters. 

3.  Tuned  as  before  to  1,500  and  400  meters  and  receiving 
from  waves  of  1,500  and  500  meters,  we  may  get  interference 
from  waves  1,500  and  400  meters.     In  this  case,  we  are  in  tun6 
with  both  waves  of  the  interference  and  the  desired  signals  may 
be   entirely   drowned   out.     This  may  be   overcome   by   simply 


Tuning — Interference  Prevention.  191 

adding  inductance  in  the  secondary  or  capacity  in  the  primary 
circuit,  either  of  which  raises  both  our  wave  lengths  to  1,600 
and  500  meters.  We  will  then  get  our  station  on  the  short 
wave  where  there  is  no  interference. 

4.  Under  the  same  conditions  as  before,  suppose  a  station 
begins  sending,  both  waves  of  which  are  of  exactly  the  same 
length  as  those  of  the  station  from  which  we  are  receiving. 
If  there  is  no  difference  in  the  tone  or  intensity  of  the  signals, 
we  must  wait  our  turn,  as  there  is  positively  no  way  of  getting 
around  this  type  of  interference.  However,  this  is,  fortunately, 
a  very  rare  case  and  will  not  often  be  encountered. 

Case  2.  When  in  tune  with  the  short  wave  length  of  the 
transmitting  station,  the  types  of  interference  are  similar  to 
those  under  Case  1,  but  the  remedies  are  slightly  different.  One 
example  will  be  given  here,  and  the  reader  may  work  out  the 
rest  for  himself. 

1.  We  are  tuned  to  1,500  and  400  meters,  and  are  receiving 
from  waves  of  1,600  and  400  meters.  Interference  of  1,400  and 
400  meters  may  be  tuned  out  by  adding  inductance  in  the  sec- 
ondary circuit  or  capacity  in  the  primary,  either  of  which  will 
raise  our  wave  lengths  to  1,600  and  500  meters.  The  desired 
signals  will  then  come  in  on  the  1,600  meter  wave. 

Questions  now  begin  to  come  up.  How  can  we  tell  to  which 
wave  we  are  tuned?  This  sounds  well  on  paper,  but  in  practice 
how  are  we  to  determine  whether  we  are  tuned  to  the  long,  to 
the  short,  or  to  both  waves?  Nothing  could  possibly  be  more 
simple.  All  we  have  to  do  is  to  add  inductance  to  the  primary 
and  observe  the  result  upon  the  intensity  of  the  signals.  If  the 
signals  are  cut  out  altogether,  we  are  in  tune  with  the  long 
wave,  if  the  signals  are  not  affected  or  are  only  slightly  de- 
creased in  audibility,  we  are  in  tune  with  the  short  wave,  and  if 
they  are  not  cut  out  entirely,  but  their  audibility  is  considerably 
diminished,  we  are  in  tune  with  both  waves. 

Is  it  not  possible  to  strengthen  weak  signals  by  these  meth- 
ods? It  certainly  is.  For  instance,  suppose  we  are  receiving 
from  1,500  and  500  meter  waves  and  are  tuned  to  1,500  and  400 
meters.  If  the  signals  are  weak,  they  may  be  strengthened  by 
first  increasing  the  inductance  in  the  secondary  until  we  are 
tuned  to  1,600  and  500  meters.  The  signals  will  then  come  in  on 
the  500  meter  waves.  Then,  by  taking  half  as  much  inductance 
from  the  secondary  as  was  added  to  it,  and  loosening  the  coup- 
ling, we  become  tuned  to  1,500  and  500  meters  and  are  getting 
energy  from  both  waves  and  consequently  stronger  signals." 

7.  Fig.  73.  Small  stations  will  find  it  an  advantage 
to  use  the  series  inductance  in  the  primary  circuit  as 
shown  when  receiving  from  stations  using  long  wave 
lengths.  This  corresponds  to  the  use  of  a  loading  coil 
at  the  transmitter. 


192 


Experimental  Wireless  Stations. 


8.  Fig.  74.  Differential  (Fessenden)  Method.  Two 
identical  loose  couplers  connected  as  shown  are  used. 
The  variometer  is  a  form  of  tuner  which  will  be  described 
later,  and  a  single  slide  tuner  may  be  used  instead.  In 
operation  the  switch  "a"  is  opened  and  the  set  is  tuned 
to  the  desired  signals.  A  is  then  closed  and  the  vario- 
meter or  single  slide  tuner  adjusted  until  the  signals  are 
received  the  loudest.  The  condenser  marked  5%  must  be 


adjusted  so  that  its  capacity  is  nearly  5  per  cent  more 
than  the  other  one.  The  interfering  impulses  are  not 
in  tune  with  either  half  of  the  circuit,  so  that  they  go 
through  both  sides  very  nearly  equally.  As  in  the  bridge 
method,  they  become  neutralized  and  do  not  affect  the 
receiver. 

9.  Fig.  75.  Simple  loop  aerial  connection.  Elimi- 
nates natural  disturbances  and  short  interfering  waves. 
When  a  looped  aerial  is  used  it  is  used  as  an  ordinary 
aerial  for  transmitting  and  a  loop  for  receiving. 


CHAPTER  XVII. 


CONSTRUCTION  OF  RECEIVING  CONDENSERS. 
FIXED  AND  VARIABLE. 

The  discussion  which  has  already  been  given  for  send- 
ing condensers  applies,  for  the  most  part,  to  receiving 
condensers.  The  main  difference  is  that  the  insulation 
for  receiving  condensers  does  not  need  to  be  so  heavy 
because  of  the  lower  potential  and  currents  used.  The 
coatings  of  receiving  condensers  are,  therefore,  placed 
very  close  together  so  as  to  secure  a  large  capacity  in  a 
small  space.  Air  is  used  for  variable  condensers  to  a 
large  extent  because  it  provides  a  convenient  dielectric 
which  has  no  hysteresis  losses.  On  account  of  the  low 
dielectric  constant,  however,  other  dielectric  materials, 
such  as  castor  oil,  mica,  paraffine  paper,  and  glass  arc 
used  whwi  large  capacity  is  desired.  The  capacities  nec- 
essary for  the  receiving  circuits,  however,  arc  generally 
small.  The  laws  for  parallel  and  series  connections  as 
stated  for  transmitting  condensers  apply  to  receiving 
condensers  as  well,  and  as  has  already  been  pointed  out  a 
fixed  and  variable  condenser  can  be  used  in  parallel,  the 
fixed  condenser  to  approximate  the  desired  capacity  and 
the  variable  condenser  to  make  up  the  difference.  This  is 
perhaps  the  most  satisfactory  and  economical  arrange- 
ment as  large  variable  capacities  are  then  unnecessary.  In 
making  fixed  condensers,  the  proper  capacity  must  be 
approximated,  and  can  be  calculated  by  the  formulas  al- 
ready given  for  transmitting  condensers.  It  is  well  to 


194  Experimental  Wireless  Stations. 

make  several  units  which  may  be  connected  in  or  out  of 
the  circuit  to  secure  a  variable  step  condenser. 

The  proper  capacity  necessary  for  each  set  must  be 
determined  experimentally,  though  the  approximate 
amount  can  be  found  by  calculation.  This  is  essential 
because  of  the  variable  quantities  concerned,  such  as  the 
other  apparatus  employed,  the  size  of  the  aerial,  etc., 
which  is  a  different  problem  than  when  the  transmitting 
condenser  is  calculated  for  a  definite  size  and  kind  of 
transformer.  The  use  of  too  little  capacity  can  generally 
be  told  by  the  weakness  of  the  received  signal.  Capacity 
should  be  added  until  the  maximum  sound  is  received.  If 
however,  an  excess  of  capacity  is  used,  the  signals,  will 
become  muddy  and  indistinct.  The  capacity  should  then 
be  lessened  until  the  ragged  sound  disappears  and  is 
clear. 

There  are  many  suitable  constructions  for  both  fixed 
and  variable  condensers,  the  designs  here  described  being 
those  most  generally  used. 

FIXED  CONDENSER. 

These  are  used  as  shunts  around  the  detector  or  phones 
to  increase  the  intensity  of  the  received  signal.  When 
tuning  inductances  having  adjustable  coils  are  used,  the 
secondary  or  detector  circuit  condenser  can  be  of  the 
fixed  or  fixed  step-by-step  type.  A  variable  condenser 
is  hardly  necessary  except  in  the  primary  or  aerial  cir- 
cuit, and  since  it  is  more  expensive,  particularly  in  the 
large  sizes,  the  step  by  step  type  is  best  to  use  in  parallel 
with  a  small  balancing  variable  condenser  as  has  already 
been  pointed  out.  Aside  from  intensifying  the  received 
signals,  a  condenser,  if  of  the  adjustable  type,  allows 
of  fine  selective  tuning. 


Construction  of  Receiving  Condensers.         195 

A  convenient  condenser  unit  which  may  be  connected 
together  with  duplicate  units  or  variable  capacity  to  se- 
cure almost  any  capacity  is  made  as  follows : 

CONSTRUCTION. 

Obtain  a  good  grade  of  bond  paper  about  .004  or  .005 
(measure  with  a  micrometer),  of  an  inch  thick  and  soak 
several  sheets  in  a  pot  of  clean  melted  paraffine  until  the 
air  bubbles  are  driven  out.  When  air  bubbles  no  longer 
rise,  hang  the  sheets  up  to  dry  and  cut  them  into  pieces 
2  inches  by  3  inches. 

The  coatings  are  made  from  tinfoil  cut  to  pieces  1  5-8 
of  an  inch  by  3  inches  long,  and  smoothed  out  by  a  roller 
as  described  for  transmitting  condensers.  * 

ASSEMBLING. 

Lay  a  strip  of  tinfoil  upon  a  strip  of  paraffined  paper 
so  that  3-8  of  an  inch  of  one  end  of  the  foil  projects 
beyond  one  of  the  long  ends  of  the  paper.  Now  lay  a 
sheet  of  paper  on  top  of  this  and  again  place  a  sheet  of 
the  foil,  but  projecting  the  3-8  of  an  inch  on  the  other 
end  of  the  paper.  Repeat,  until  the  desired  number  of 
sheets  and  foil  have  been  alternately  arranged,  six  or 
eight  sheets  being  a  desired  number.  The  foil  should 
be  arranged  evenly  between  the  paper,  so  that  the  margin 
on  three  sides  is  nearly  equal.  When  done,  the  condenser 
should  consist  of  alternate  layers  of  foil  and  paper  with 
every  other  foil  projection  on  an  opposite  end  of  the 
paper.  Now  place  the  assembled  condenser  between  two 
temporary  boards  and  a  clamp  and  squeeze  together  under 
the  influence  of  heat.  This  may  be  accomplished  over  a 
hot  air  or  steam  register  or  open  oven  which  is  just  hot 


196  Experimental  Wireless  Stations. 

enough  to  soften  the  paraffine  of  the  paper  sheets.  Tighten 
up  the  clamps  and  remove  them  after  the  wax  cools.  The 
two  sets  of  connecters  are  then  soldered  or  clamped  to  a 
conductor  of  stranded  copper  wire,  and  may  be  mounted 
in  almost  any  desired  manner.  The  condenser  used  as  a 
detector  shunt  may  be  mounted  in  the  base  of  the  de- 
tector stand.  Switches  should  be  provided  for  connect- 
ing several  of  these  units  in  series,  parallel,  or  series  mul- 
tiple. About  three  of  these  units  in  parallel  will  be  the 
right  amount  for  the  chopper  condenser  of  the  continuous 
wave^receiving  set,  while  a  single  unit  will  suffice  for  most 
of  the  secondary  or  detector  circuits.  Test  as  described 
for  the  transmitting  condenser.  The  condenser  should 
hold  the  battery  charge  for  some  little  time  and  should 
be  capable  of  discharging  through  the  telephone  receiver 
with  an  audible  click  several  seconds  after  the  battery 
terminals  have  been  disconnected  from  it.  It  is  seldom 
that  this  kind  of  condenser  is  burnt  out  or  injured,  so 
that  once  made,  it  is  practically  permanent.  The  primary 
condenser  for  the  spark  coils  already  described  is  built 
in  the  same  manner,  except  that  the  larger  dimensions 
given  are  used.  A  shunt  condenser  around  a  telegraph 
key  used  for  sending,  should  have  a  large  capacity  sim- 
ilar to  that  used  around  the  vibrator  contacts  of  a  coil. 
Paraffined  tissue  paper  such  as  is  used  to  wrap  eatables 
and  instruments  may  be  had  ready  paraffined  and  is  de- 
sirable because  of  the  uniform  thickness.  The  condenser 
can  also  be  assembled  by  applying  the  foil  to  the  paper 
while  the  wax  is  still  soft  and  warm,  making  the  after- 
warming  and  pressure  unnecessary. 

KORDA  AIR  CONDENSER. 

This  type  of  variable  condenser  is  in  general  use 
for  wireless  receiving  sets,  wave  meters,  and  is  partic- 


Construction  of  Receiving  Condensers.          19? 

ularly  desirable  in  the  primary  or  aerial  circuit  for  tuning 
purposes.  Fine  adjustment  is  possible  and  when  properly 
made  there  is  little  or  no  loss  in  the  condenser.  The 
construction  is  somewhat  difficult,  however,  but  since  the 
plates  may  be  had  already  cut  and  smoothed,  the  main 


TVvst  Washer 
ibf« 


FIC.-7B. 


ibt-c 


difficulty  is  limited  to  the  arrangement  of  the  plates.  It 
is  not  necessary  to  use  a  large  number  of  plates  provided 
the  arrangement  with  a  parallel  step  by  step  condenser 
is  adopted.  Such  a  step  by  step  condenser  should  not 
have  more  than  one  or  two  sheets  of  foil  and  dielectric 


198  Experimental  Wireless  Stations. 

to  each  unit  or  step  and  the  switch  contacts  used,  should 
be  good  and  well  cleaned. 

The  plates  used  should  be  of  brass  or  aluminum  of 
about  No.  20  B&S  gauge  and  since  the  cutting  is  difficult 
to  do  by  hand,  they  are  preferably  purchased  already 
stamped  from  supply  houses  or  else  turned  out  in  a 
lathe  by  a  machinist.  It  is  essential  that  the  plates  be 
perfectly  flat  and  even.  The  number  of  plates  used 
need  not  be  more  than  four  or  six  if  a  fixed  condenser 
in  parallel  is  also  used,  but  if  the  condenser  is  to  be  used 
alone,  from  twenty-four  to  twelve  plates  should  be  used. 
This  is  for  the  larger  or  stationary  plates,  one  less  being 
used  for  the  rotary  plates.  Five  fixed  and  four  rotary 
plates  make  a  convenient  size  for  a  variable  unit. 

The  five  fixed  plates  should  be  semi-circles  5j4  inches 
in  diameter  and  the  rotary  plates  of  which  four  are  need- 
ed should  be  4J^  inches  in  diameter,  as  these  are  standard 
sizes.  It  will  be  understood  that  larger  units  may  be 
made  in  the  same  manner,  using  more  plates.  The  sev- 
eral details  are  shown  in  fig.  76.  The  five  large  semi- 
circles should  be  placed  together  and  three  5-32  in.  holes 
drilled  near  the  edge  as  shown  at  (A).  The  four  small 
plates  are  placed  in  the  same  manner,  except  that  only 
one  5-32  inch  hole  is  bored  as  shown. 

Obtain  brass  or  copper  washers  5-32  inch  thick,  3-8 
of  an  inch  in  diameter  and  with  a  5-32  inch  hole  at  the 
center.  These  may  be  had  at  a  supply  house  or  hard- 
ware store.  Also  obtain  some  5-32  inch  brass  rods. 

ASSEMBLING  THE  ROTARY  PLATES. 

The  plates  are  assembled  after  the  holes  have  been 
smoothed  and  burrs  removed,  by  passing  a  piece  of  the 
5-32  inch  rod  alternately  through  a  plate  and  then  a 


Construction  of  Receiving  Condensers.         199 

washer.  The  ends  of  the  rod  should  be  threaded  with  an 
eight  thirty-two  die  and  the  rod  cut  so  that  a  short  exten- 
sion is  left  beyond  the  plates  for  a  handle.  The  plates 
are  held  together  on  the  rod  by  two  threaded  washers  or 
nuts  l/2  inch  in  diameter  and  9-32  of  an  inch  thick.  The 
nuts  should  be  turned  tightly  so  that  the  plates  can  not 
move  after  they  are  placed  in  alignment. 

ASSEMBLING  THE  FIXED  PLATES. 

A  similar  plan  is  used  with  the  fixed  plates,  a  rod 
being  inserted  in  each  of  the  three  holes,  and  threaded 
8-32  at  the  ends  as  before,  care  being  taken  to  keep  the 
plates  in  alignment.  The  washers  between  the  plates  are 
placed  at  all  three  positions.  A  longer  extension  should 
be  left  on  these  rods  for  fastening  purposes.  The  appear- 
ance of  the  assembled  plates  is  shown  at  (B)  of  the  figure. 

Obtain  two  pieces  of  fibre  3-16  of  an  inch  thick  and 
cut  out  two  pieces  with  the  shape  and  having  holes  as 
shown  at  (C).  The  holes  1,  2,  3,  correspond  to  the  holes 
of  the  large  plates,  and  the  hole  4  is  bored  so  that  when 
the  shaft  of  the  movable  plates  is  in  place  in  it  and  the 
fibre  is  assembled  on  the  rods,  the  brass  washers  of  the 
movable  plates  will  not  touch  or  make  contact  with  the 
fixed  plates.  This  is  important,  as  a  short  circuit  would 
result  otherwise.  About  l/2  inch  will  be  sufficient  exten- 
sion for  this  hole.  The  lower  fibre  piece  is  held  in  place 
on  the  rods  by  8-32  nuts.  It  is  preferably  spaced  a  little 
distance  from  the  lower  plate  by  washers.  The  upper 
fibre  piece  is  similarly  placed  after  the  plates  have  been 
placed  in  position. 


200  Experimental  Wireless  Stations. 

ASSEMBLING  AND  MOUNTING. 

The  assembled  plates  must  not  rub  or  touch  each 
other  and  must  be  brought  into  alignment,  the  adjustable 
screw  bearing  at  the  bottom  shown  at  (D)  being  a  suit- 
able means.  The  rotary  plates  can  be  raised  or  lowered 
by  this  arrangement.  The  condenser  may  be  suitably 
mounted  in  a  box  or  case,  and  the  connections,  one  from 
a  washer  on  the  fixed  plates  and  one  from  a  brass  strip 
or  brush  bearing  on  the  rotary  shaft  near  the  top,  may 
be  brought  to  binding  posts.  The  excess  length  of  the  rods 
can  then  be  cut  off,  and  a  handle  provided  for  the  ro- 
tary shaft.  A  scale  and  pointer  can  also  be  arranged 
on  the  cover,  to  suit.  Electrose  or  composition  knobs 
such  as  are  used  for  typewriter  platens  (obtainable  at 
supply  houses)  make  good  handles  for  this  purpose.  The 
scale  may  be  calibrated  by  comparison  with  a  known 
standard,  using  a  wave  meter,  or  may  be  arbitrary,  using 
equal  divisions.  A  brass  protractor  such  as  is  used  by 
draughtsmen  may  be  had  for  a  few  cents  and  makes  a 
convenient  scale.  The  pointer  can  be  cut  out  of  a  strip 
of  brass  or  aluminum.  Two  or  more  of  these  units  may 
be  mounted  in  a  common  case  or  box  and  switches  pro- 
vided for  changing  the  connections.  Moving  washers 
are  preferably  provided  at  the  upper  bearing  to  take  up 
the  thrust,  so  that  the  condenser  may  be  used  in  any 
position.*  When  neatly  carried  out  this  type  of  con- 
denser will  be  of  business  like  appearance  as  well  as 
operation. 

MAKESHIFTS. 

It  is  often  desired  to  have  a  simple  makeshift  variable 
condenser  for  experiments.  Almost  any  two  conductors 


A  horizontal  position  for  the  axis  is  not  desirable. 


Construction  of  Receiving  Condensers.         201 

in  any  shape  separated  by  any  dielectric,  so  that  more 
or  less  surface  may  be  brought  into  relation  to  form  capa- 
city, are  suitable.  Such  common  things  as  tin  cans  may 
be  utilized,  the  insulation  being  provided  by  using  paper 
or  even  a  coat  of  shellac  or  asphaltum.  A  can  painted 
in  this  manner  and  suspended  so  that  its  height  in  a  jar  of 
salt  water  can  be  altered,  connections  being  made  to  the 
can  and  to  a  plate  inserted  in  the  solution,  is  suitable, 
provided  that  every  part  of  the  exposed  surface  is  cov- 
ered by  a  thin  coat  of  the  insulating  varnish.  Sliding 
plates  similar  to  those  described  for  a  variable  sending 
condenser  may  also  be  used.  Two  tin  cans  having  dia- 
meters so  that  one  just  slides  into  the  other  after  a  layer 
of  paper  has  been  shellaced  on  the  inner  or  sliding  one. 
may  be  used.  Similar  arrangements  will  doubtless  sug- 
gest themselves  to  the  reader  and  if  carried  out  care- 
fully may  serve  quite  well.  The  series  capacity  used  in 
the  aerial  circuit  should  have  a  comparatively  large  capa- 
city. This  is  best  obtained  by  using  a  fixed  and  a  variable 
capacity  in  parallel,  in  which  case  a  makeshift  arrange- 
ment carefully  constructed  will  generally  have  sufficient 
capacity  to  make  it  of  considerable  use. 

The  Korda  condenser  described  is  desirable,  however, 
and  if  immersed  in  a  can  of  transformer  or  castor  oil, 
preferably  the  latter,  its  capacity  will  be  considerably 
increased.  (See  chapter  on  the  calculation  of  capacity). 
The  maximum  capacity  of  such  a  condenser  is  readily  cal- 
culated when  the  area  is  taken  by  using  the  formula. 

Area  of  a  circle  =  3.1416  R2  taking  the  radius  R  for 
the  rotary  plates,  and  dividing  by  2  to  find  the  area  of  the 
half  circle. 


CHAPTER  XVIII. 


CONSTRUCTION  OF  TUNING  INDUCTANCES. 

LOOSE  COUPLERS,  VARIOMETERS, 

TUNERS. 

GENERAL  REQUIREMENTS. 

Whatever  type  of  tuning  is  adopted,  the  inductances 
used  should  be  carefully  constructed  with  accurate  and 
delicate  adjustments.  Every  part  should  be  nicely  made 
and  great  care  taken  with  the  insulation  and  contacts. 
The  cores  and  ends  used  are  preferably  made  from  hard 
rubber,  fibre  or  molded  composition,  but  wood  and  paper 
when  dry  and  carefully  shellaced  may  be  substituted.  The 
wire  used  should  be  uniform,  and  may  either  be  bare  or 
insulated.  Bare  wire  is  spaced  by  means  of  a  thread  or 
a  groove  cut  into  the  core,  while  insulated  wire  is  sep- 
arated naturally.  Contact  is  best  made  when  bare  wire 
is  used.  Enameled  wire  is  neat  and  useful  since  a  con- 
tact portion  is  readily  scraped  from  the  wire.  Cotton  and 
silk  insulations  are  difficult  to  scrape  for  contact  with 
sliders,  so  that  the  job  is  neat  and  effective.  The  only 
objection  to  enameled  wire  seems  to  be  that  the  turns 
are  brought  too  close  together,  so  that  an  undesirable 
electrostatic  capacity  is  formed  between  the  adjacent 
turns.  Wood  may  be  used  for  bases.  All  metallic  parts 
including  connecting  wires  should  be  carefully  insulated 
from  each  other  and  even  from  wood,  by  using  hard 
rubber  sheeting  and  tubes.  In  receiving  delicate  and 


Construction  of  Receiving  Condensers.         203 

minute  oscillations  from  distance  stations,  every  detail 
counts  for  efficiency  and  too  much  care  cannot  be  taken 
if  the  maximum  results  are  desired.  Holes  are  prefer- 
ably filled  up  with  tar  or  wax,  and  shields  provided  to 
prevent  injury  or  leakage  to  or  from  the  wires.  In  the 
following  designs,  descriptions  will  be  given  for  induct- 
ances of  standard  design  and  merit  and  while  there  are 
varied  forms  for  the  detailed  constructions,  and  much 
ingenuity  can  be  exercised,  the  main  dimensions  and  de- 
sign should  generally  be  adhered  to,  to  secure  efficient 
instruments. 

TUNERS,  SLIDE  TYPE.- 

This  form  is  commonly  employed  for  tuning,  bridge, 
loading,  and  similar  methods  as  has  already  been  de- 
scribed. While  only  one  slider  is  described,  it  will  be 
understood  that  duplicate  sliders  can  be  provided  on 
other  parts  of  the  circumference  of  the  core  and  wire 
It  is  well  to  provide  binding  posts  for  the  wire  terminals 
in  every  case  so  that  a  variety  of  utility  is  the  result.  (See 
fig.  77.) 

Core.  This  may  be  turned  out  from  hard  wood,  but 
since  wood  shrinks,  a  rubber,  fibre,  composition,  or  even 
a  shellaced  paper  tube  is  much  prefered.  Suitable  tubes 
may  be  had  from  supply  houses.  Paper  or  fibre  tubes 
can  be  made  by  rolling  up  and  gluing  a  sheet  of  the  thin 
fibre  into  the  desired  size.  Hollow  tubes  have  the  addi- 
tional advantage  of  light  weight.  The  diameter  of  the 
tube  may  be  any  convenient  size  between  2l/2  inches  and 
6  inches,  the  smaller  diameters  providing  sharper  ad- 
justment. 3J/2  inches  is  a  desirable  diameter.  If  bare 
wire  is  to  be  used  on  the  fibre,  rubber  or  composition 
tube,  it  is  very  desirable  to  turn  or  have  a  machinist 


204 


Experimental  Wireless  Stations. 


turn  a  thread  on  the  core.  About  18  threads  to  the  inch 
makes  a  suitable  thread  for  use  with  No  22  wire,  which 
is  a  common  size  in  favor.  The  threads  can  be  cut  to 
within  J/2  inch  or  so  from  each  end.  The  length  of  the 
tube  used  may  be  from  3  inches  to  12  inches  or  more  as 
desired. 

The  winding.  Use  soft  copper  wire  of  not  more  than 
No.  24  in  fineness,  nor  less  than  No.  18  in  coarseness, 
No.  20  or  22  being  preferred.  The  winding  can  be  done 
by  hand  if  care  is  taken,  but  a  lathe  or  makeshift  lathe 


Rod 


SJid«r 


Hole  for  3cr«w. 


»•*> 


RE.TQ. 


is  best  to  use.  The  wire  should  be  wound  tigntly  and 
evenly,  avoiding  kinks.  When  the  core  is  threaded,  this 
is  easy.  If  bare  wire  is  used  without  threading  the  core, 
the  turns  should  be  spaced  by  winding  the  wire  with  a 
turn  of  heavy  linen  thread,  so  that  each  turn  is  spaced 
by  the  thickness  of  the  thread  and  the  adjacent  turns  of 
wire  do  not  touch  each  other.  Enameled  wire  is  wound 
without  spacing.  Cotton  or  silk  insulation  is  not  recom- 
mended for  wire  for  tuners  of  this  type.  The  bare  wire 
is  preferred.  Then  ends  of  the  wire  can  be  fastened  by 
means  of  a  small  hole  drilled  at  the  end  of  the  core  or  else 
by  means  of  a  small  screw.  If  hard  drawn  copper  wire, 


Construction  of  Tuning  Inductances.  205 

such  as  may  be  had  at  hardware  stores,  is  available,  it  is 
preferred  as  it  is  more  durable  and  easier  to  wind. 

CORE  ENDS.— BASE 

While  the  core  ends  must  be  of  a  size  corresponding  to 
the  diameter  of  the  tube  used,  which  may  vary  from  2  in. 
to  6  in,  a  margin  should  be  provided  to  allow  for  clearance 
from  a  base,  sliders,  and  so  on.  The  ends  are  preferably 
square  and  may  be  easily  fastened  to  the  cores  in  any 
desired  manner.  For  solid  wood  cores,  wood  screws  may 
be  used.  Tubings  are  best  fastened  by  turning  a  recess 
in  the  inner  end  of  the  core  end  which  will  fit  over  the 
tube  snugly.  Another  method  is  to  provide  plug  ends 
for  the  tube,  which  are  then  screwed  on  the  core  ends. 
When  assembled,  the  tuner  should  set  true.  The  use 
of  a  base  is  optional  and  is  hardly  necessary,  except  for 
appearance  and  possibly  convenience.  The  binding  posts 
can  be  brought  out  on  the  core  ends. 

SLIDERS. 

(See  fig.  78).  These  may  be  any  suitable  type  which 
will  make  a  step  by  step  contact  with  the  several  turns 
of  wire  without  undue  friction.  The  slider  rods  arc 
preferably  of  square  or  rectangular  shape,  as  round  rods 
must  be  used  doubly  to  prevent  undesired  turning.  The 
rod  is  cut  as  long  as  the  length  of  the  core  plus  the  thick- 
ness of  the  core  ends,  which  should  not  be  over  ^  inch, 
plus  a  little  extra  for  connections  or  a  binding  post.  While 
only  one  form  of  slider  is  shown,  to  avoid  unnecessary 
duplication,  it  will  be  understood  that  many  other  forms 
may  be  used.  The  essential  feature  of  sliders  is  that 
they  should  make  good  contact  with  only  one  turn  of  wire 


206  Experimental  Wireless  Stations. 

at  a  time  and  without  too  much  friction.  If  the  slider 
touches  two  turns  at  once  (which  will  happen  if  care  is 
not  taken),  the  turn  is  short  circuited.  This  is  not  de- 
sirable as  the  intensity  of  the  received  signals  is  thus 
lessened.  The  spiral  spring  shown  can  be  coiled  from 
No  22  spring  brass,  and  a  round  piece  of  copper  wire 
smoothed  off  to  a  round  surface  is  soldered  on  the  tip. 
The  length  of  the  spiral  should  be  enough  to  make  contact 
with  the  wire  after  the  slider  is  in  place.  While  con- 
nection with  the  slider  can  be  made  through  the  rod  by 
the  sliding  contact  which  results,  this  method  is  not  desir- 
able and  a  flexible  insulated  wire  is  best  soldered  directly 
to  the  slider.  The  knob  is  for  convenience  in  handling, 
and  can  be  made  from  hard  rubber  or  purchased  already 
molded.  Sliders  and  rods  may  be  had  in  the  open  market. 
The  slider  should  slide  on  the  rod  without  sticking.  Load- 
ing coils  may  be  made  without  sliders,  by  taking  taps  off 
from  every  ten  or  twenty  turns  and  using  multi-point 
switches.  The  wire  when  wound  on  smooth  forms  should 
be  coated  with  two  coats  of  shellac  and  allowed  to  dry. 
The  portion  for  contact  is  then  scraped  clean  for  a 
distance  along  the  length  of  the  coil  and  under  the  slider, 
of  about  y2  inch.  This  may  be  accomplished  by  using  a 
knife  or  a  small  block  of  wood  covered  with  emerv  cloth. 
The  wire  should  be  scraped  until  it  shows  clean  and 
bright.  Two  wooden  strips  may  be  temporarily  fastened 
on  the  core  the  desired  distance  apart  to  serve  as  a  guide 
so  that  the  scraped  portion  will  be  of  uniform  width. 
If  several  sliders  are  used,  two  may  be  taken  from  the 
top  or  one  from  each  side,  or  all,  as  desired.  The  use 
of  bare  wire  wound  in  a  threaded  tube  core  is  best  adopted 
for  a  standard,  the  diameter  being  3  inches  and  length 
10  inches,  as  this  will  give  a  serviceable  instrument  with 
a  wide  range  of  utility.  Wires  wound  on  smooth  cores 


Construction  of  Tuning  Inductances. 


207 


or  wood  cores,  particularly  enamelled  wire,  tend  to  loosen 
after  a  time,  in  which  case  it  is  best  to  either  rewind  the 
coil  or  make  a  new  one. 

VARIOMETER. 

A  variometer  is  a  form  of  tuner  without  any  sliding 
or  variable  contacts  and  depends  solely  on  the  variable 
coupling  between  its  two  parts  which  are  connected  to- 
gether. It  is  quite  easily  made  and  is  very  useful  in 


Wire 


connection  with  other  apparatus,  particularly  as  a  loading 
coil.    It  may  be  used  alone  for  short  wave  lengths. 

A  suitable  construction  is  indicated  in  fig.  79.  The 
cores  are  of  hollow  fibre,  rubber,  composition  or  paper 
and  may  be  made  as  has  already  been  described.  One 
core  (the  stationary  core)  is  6  in.  in  diameter  and  21-8 
inches  wide,  while  the  inner  and  movable  core  is  4  7-8 
inches  in  diameter  and  21-8  inches  wide.  The  larger 
core  is  wound  with  about  forty  feet  of  No.  22  insulated 
wire,  so  that  a  space  of  l/i  inch  is  left  at  the  center.  This 
will  make  about  24  turns  on  each  side  of  the  space.  The 
small  core  is  wound  in  the  same  way,  except  that  28  turns 


208  Experimental  Wireless  Stations. 

are  wound  on  each  side  of  the  space.  Both  parts  of 
each  core  should  have  the  same  number  of  turns. 

J4  in-  holes  are  now  bored  or  punched,  at  opposite 
points  of  the  two  cores,  in  the  center  of  the  J^  inch  bare 
band,  for  a  rod.  This  rod  is  a  piece  of  J4  mcn  round 
brass  7j^  inches  long,  and  is  passed  through  the  holes  as 
shown  in  the  figure.  Now  take  a  piece  of  No.  18  bare 
wire  about  Sl/2  inches  long  and  fasten  it  as  shown,  solder- 
ing it  at  the  center  to  the  J4  mcn  rod  and  bringing  the 
ends  through  the  small  core.  This  is  to  make  the  inner 
coil  fast  to  the  rod  so  that  it  may  be  rotated.  Rubber  or 
fibre  washers  (W)  should  be  placed  as  shown,  so  that 
the  inner  coil  is  free  to  rotate  within  the  outer  coil.  The 
two  coils  are  connected  together  as  shown  with  a  short 
length  of  flexible  insulated  wire. 

Mounting.  This  may  be  carried  out  as  desired,  a  box 
6^2  inches  cube  being  suitable.  Binding  posts  should  be 
provided  and  connections  made  so  that  starting  with  the 
end  of  one  coil,  the  wire  continues  until  the  opposite  end 
of  the  other  coil  is  reached  at  the  other  binding  post. 
A  knob  with  a  pointer  and  a  scale  may  be  provided  as 
described  for  the  variable  condenser  of  chapter  17.  Use 
like  a  tuning  or  loading  coil.  When  at  right  angles  the 
two  coils  are  neutral,  while  when  concentric  the  closest 
coupling  adjustment  is  reached.  About  75  feet  of  the 
wire  will  be  needed.  The  coils  may  be  shellaced  and  the 
instrument  finished  as  desired.  In  mounting  the  instru- 
ment, the  outer  coil  is  fastened  rigidly  to  the  case  or  cover 
so  that  only  the  inner  coil  is  rotable. 

LOOSE  COUPLER. 

The  loose  coupler  is  in  general  favor  at  the  present 
time,  as  with  it  and  condensers,  a  wide  variety  of  tuning 
and  coupling  is  possible.  The  set  can  be  tuned  to  either 


Construction  of  Tuning  Inductances. 


209 


the  long  or  short  waves  or  both  and  when  the  maximum 
point  is  found  the  interfering  stations  can  often  be  tuned 
out  by  making  the  coupling  very  small.  (That  is,  pull- 
ing the  primary  far  away  from  the  secondary  or  vice 
versa.)  The  following  design  and  data  is  for  one  of 
these  instruments  and  two  will  be  required  if  the  Fessen- 
den  differential  method  is  employed.  (See  fig.  80.) 


FlE.flD. 


RE. 


PRIMARY. 

Core :  Insulating  tube  3  inches  in  diameter  and  4  5-8 
long.  The  wall  should  not  be  more  than  1-8  inch  thick. 
Wind  as  directed  for  tuner,  using  either  No.  20  or  22 
B&S  gauge  bare  or  enameled  wire,  preferably  the  for- 
mer, in  threaded  grooves.  Start  winding  9-16  of  an  inch 
from  one  end  and  wind  until  within  9-16  of  the  other  end. 


210  Experimental  Wireless  Stations. 

Heads  for  Primary.  y2  in.  thick,  4x4^  in.,  smoothed 
on  all  sides.  Find  the  center  of  each  piece  (two  needed). 
These  pieces  are  now  centered  in  a  chuck  in  a  lathe  so 
that  the  lathe  center  is  J4  mcn  below  the  marked  center  of 
the  pieces.  One  piece  is  made  with  a  hole  3  inches  in 
diameter  through  it,  while  the  other  piece  is  only  bored, 
with  this  same  size,  to  have  a  depth  of  3-8  of  an  inch. 
When  done,  one  piece  will  have  a  hole  3  inches  in  dia- 
meter through  it  while  the  other  will  have  a  smaller  hole 
coming  within  1-8  inch  of  the  other  surface. 

Base.  Three-fourths  of  an  inch  thick,  6  inches  wide 
and  16  inches  long.  (Hardwood.)  Mount  the  primary 
at  one  end  so  that  it  sets  true  and  is  nicely  spaced,  using 
screws  driven  from  the  bottom  of  the  base  into  the  heads, 
the  screws  being  countersunk.  A  single  slider  may  now 
be  provided,  as  shown  and  as  has  been  described  for 
tuners.  It  is  understood  that  the  primary  core  with  the 
winding,  is  mounted  in  the  heads,  using  cement,  so  that 
the  core  and  wire  are  held  in  the  openings  in  the  heads 
and  so  that  the  head  with  the  hole  all  the  way  through 
it  faces  toward  the  long  end  of  the  base.  (See  figure.) 
SECONDARY. 

Core.  Hardwood  cylinder  turned  from  dry  wood.* 
Diameter,  2j/£  inches.  Length,  5  inches.  (See  fig.  80.) 
Have  a  machinist  mill  a  slot  3-16  wide  by  3-8  deep  as 
shown  at  (a)  the  whole  length  of  the  core.  This  should 
be  smooth  when  done.  Inasmuch  as  bare  wire  is  to  be 
used,  it  would  be  well  to  have  threads  turned  on  the 
cylinder  before  the  milling  is  done.  These  should  be  20 
to  the  inch,  and  very  light.  Wind  with  No.  26  B&S  hard 
drawn  copper  wire.  Threads  may  be  used,  spacing  the 
turns  with  linen  thread,  if  the  machine  threads  cannot 

*  A  hollow  tube  may  be  used  if  a  frame  is  provided 
for  the  slot. 


Construction  of  Tuning  Inductances.  211 

be  cut.  Use  considerable  pressure  in  winding,  as  the  con- 
tact is  to  be  made  from  below.  The  linen  thread  used 
should  be  about  as  thick  as  the  wire  used.  Start  £4  mc^ 
from  one  end  and  wind  to  3-8  inch  of  the  other. 

Head.  One  needed.  ^4  mcn  stock,  cut  3^4  inches 
square  with  a  hole  bored  in  center  to  a  depth  of  3-8  of 
an  inch.  This  hole  is  2^  inches  in  diameter  and  is  turned 
as  before. 

Attach  the  head  to  the  secondary  core  at  the  24  m-  end 
by  small  screws  started  from  the  back  of  the  head  and 
screwed  into  the  core.  The  secondary  slider  is  made  so 
that  more  or  less  wire  is  included  in  the  circuit  when  the 
rod  (See  b)  is  moved  in  or  out,  and  allows  of  adjust- 
ment after  the  secondary  is  within  the  primary  coil.  This 
slider  is  made  from  a  piece  of  5-32  inch  brass  rod,  7 
inches  long,  to  one  end  of  which  a  small  loop  of  thin 
spring  brass  5-32  inch  wide,  is  soldered,  as  shown.  A 
rounded  point  is  then  soldered  on  the  upper  part  of  this 
spring  to  make  contact  with  a  single  turn  of  wire  at  a 
time.  Note  the  notch.  This  is  made  by  a  few  strokes 
with  a  fine  three  cornered  file.  A  handle  is  provided  at 
the  other  end  of  the  rod.  The  slider  is  mounted  in 
the  milled  slot  and  extends  through  the  head  through  a 
small  hole. 

MOUNTINGS. 

The  mountings  are  shown  clearly  in  the  figure.  Bind- 
ing posts  should  be  provided  and  flexible  insulated  wires 
should  be  brought  to  the  slider  rods.  The  inner  end  of 
the  secondary  coil  can  be  brought  to  the  back  by  either 
boring  a  hole  through  the  cylinder  or  else  making  a  groove 
in  one  side  of  the  milled  slot  so  that  the  wire  imbedded  in 
it  cannot  possibly  make  contact  with  the  slider.  Both 
ends  of  both  primary  and  secondary  should  be  brought 
out  to  binding  posts.  The  two  pieces  of  tubing  which  act 
as  bearings  to  support  the  secondary  have  an  internal 


212  Experimental  Wireless  Stations. 

diameter  of  J4  inch  and  are  \y2  inches  long.  They  are 
forced  into  holes  drilled  in  the  secondary  head.  The 
rods  on  which  the  secondary  slides  are  10^2  inches  long 
and  are  supported  as  shown,  one  end  being  fastened  by 
passing  through  holes  in  the  inner  head  of  the  primary 
and  the  other  end  being  fastened  to  a  small  bridge  fas- 
tened to  the  base.  The  latter  is  1x1x4  inches  long. 
Small  nuts  serve  to  hold  the  rods  in  place.  The  coils 
should  be  mounted  so  that  the  secondary  will  slide  freely 
into  the  primary.  The  remainder  of  the  instrument  is 
left  to  the  individual  worker  and  presents  no  difficulty. 
Provided  that  the  general  dimensions  are  preserved,  any 
suitable  mounting  may  be  used.  In  using  two  of  these 
with  a  Fessenden  interference  preventing  circuit,  the  con- 
denser marked  5  per  cent  must  be  calibrated  so  that  it 
is  always  5  per  cent  different  in  capacity  than  the  other 
one.  This  may  be  accomplished  by  arranging  the  scale 
on  this  capacity  so  that  when  the  pointer  is  on  zero,  the 
condenser  will  really  be  in  mesh  to  approximately  5  per 
cent.  This  need  only  be  approximated. 

A  receiving  loose  coupler  can  be  made  on  the  pancake 
plan  using  two  flat  spirals  of  wire,  one  of  which  is  ad- 
justable with  respect  to  the  other,  as  for  the  transmitting 
oscillation  transformer.  The  spacing,  however,  is  ac- 
complished by  using  a  thin  insulated  wire  strip  such  as  is 
used  for  transformer  coils,  and  the  turns  can  be  close 
together  on  account  of  the  low  potentials  used.  Such  an 
arrangement  has  very  little  if  any  advantage  over  the 
loose  coupler  described,  particularly  if  a  variometer  is  also 
used,  so  the  duplicated  description  will  be  omitted.  The 
method  of  using  the  apparatus  described  has  already  been 
fully  set  forth. 

The  reader  with  limited  tools  can,  of  course,  make  a 
simpler  arrangement.  It  is  possible  to  make  tuning  in- 
struments with  little  or  no  facilities  and  tools. 


CHAPTER  XIX. 


CONCLUSION.    THE  RIGHTS  OF  THE  EXPERI- 
MENTER. 

The  completed  receiver,  of  whatever  type  adopted 
can  all  be  mounted  together  if  desired.  In  any  case  the 
connections  used  should  be  of  stranded  insulated  conduc- 
tors, kept  free  from  each  other,  well  insulated  from  wood 
and  other  matter,  the  switch  contacts  clean,  and  so  on. 
The  descriptions  have  been  made  as  clear  and  concise  as 
possible,  though  the  details  have  been  purposely  left  to 
the  individual  in  many  cases  where  the  design  is  optional. 
Such  items  as  cases,  boxes  or  mountings  are  well  within 
the  limits  of  every  reader,  and  even  in  the  other  apparatus 
and  parts  considerable  ingenuity  may  be  used.  Duplica- 
tion of  apparatus  has  been  avoided  wherever  possible, 
though  in  some  cases  all  forms  have  been  described.  The 
author  believes  that  when  one  piece  of  apparatus  will  do 
the  work  of  two,  there  is  little  use  in  using  two.  Every 
piece  of  apparatus  should  be  made  with  care  and  should 
always  be  understood.  Learn  to  know  your  apparatus, 
master  its  peculiarities,  note  the  good  and  bad  adjust- 
ments, always  be  on  the  lookout  for  possible  phenomena, 
and  keep  a  record  of  your  experiments.  While  the  ap- 
paratus described  is  intended  particularly  for  stations  it 
can  be  easily  made  portable.  Stations  may  be  readily  set 
up  on  small  boats,  in  the  field,  camp,  and  so  on.  There  is 
hardly  a  limit  to  the  use  to  which  a  wireless  set  may  be 
put. 


214  Experimental  Wireless  Stations. 

The  experimenter  generally  plans  to  receive  over  a 
much  greater  distance  than  he  expects  to  send.  Indeed, 
with  the  present  network  of  high-powered  stations,  there 
are  few  readers  who  may  not  do  long  distance  work  with 
even  simple  apparatus.  The  new  Arlington  station,  for 
instance,  should  be  heard  by  every  experimenter  within 
1,000  to  3,000  miles  under  favorable  conditions.  It  is 
surprising  to  learn  what  can  be  done  with  even  home 
made  apparatus.  A  list  of  wireless  stations  may  be  ob- 
tained for  15c  by  addressing  the  Superintendent  of  Docu- 
ments, Washington,  D.  C. 

If  you  have  not  already  done  so,  join  a  local  wireless 
club.  Nearly  every  locality  has  one  or  is  forming  one 
and  there  is  little  or  no  expense  attached.  If  you  have 
not  yet  learned  a  code,  start  now.  The  continental  code 
is  in  general  favor  and  it  is  well  to  master  it  first.  There 
are  so  many  messages  which  can  be  read  with  a  simple 
receiving  set,  that  the  code  can  be  mastered  in  a  short 
time.  In  practice,  it  is  well  to  start  with  the  letters  first, 
then  with  short  words,  and  finally  with  simple  sentences 
and  paragraphs.  The  average  person  finds  it  much  easier 
to  send  than  to  receive.  Acquire  a  free,  easy  and  clear 
movement  in  making  the  dots  and  dashes.  Speed  is  a 
secondary  matter,  as  it  will  come  with  practice.  It  is 
worth  while  to  keep  a  record  of  all  messages  in  a  small 
note  book. 

THE  EXPERIMENTER'S  RIGHTS. 

All  of  the  leading  countries  have  laws  regulating 
radiocommunication.  The  wireless  law  enacted  on  De- 
cember 13,  1912,  makes  the  following  restrictions  upon 
experimenters : 

1.  The  law  recognizes  the  experimenter,  gives  him  rights, 
and  licenses  are  to  be  given  provided  that, 


The  Experimenter's  Rights.  215 

2.  The  experimenter  does  not  use  a  wave  length  over  200 
meters  long  for  transmission  nor  a  greater  power  in  either  a 
coil  or  transformer  than  1  K.  W.,  if  he  is  farther  than  5  nauti- 
cal miles  away  from  a  government  station,  or  not  more  than 
Y*  K.  W.  if  he  is  within  5  nautical  miles  of  a  government 
station. 

3.  Experimenters  having  apparatus  which  is  not  powerful 
enough  to  transmit  farther  than  the  boundaries  of  the  state  in 
which  the  station  is  situated,  and  which  cannot  interfere  with 
the  reception  of  signals  from  outside  the  state,  need  not  take 
out  a  license  unless  they  desire  to  do  so.     This  means  practi- 
cally that  if  you  live  in  the  heart  of  say  Texas,  you  may  use 
large  power  without  license  provided,  stations  in  other  states 
cannot  hear  you,  but  if  you  live  near  the  border  of  another 
state  you  must  use  very  weak  power  or  else  obtain  a  license. 

4.  It  is  not  necessary  to  have  a  license  for  a  receiving 
station  only. 

5.  If  the  experimenter  wishes  to  use  a  high  wave  length 
or  high  power,  permission  will  be  granted  by  the  Secretary  of 
Commerce  and  Labor,  upon  proper  application,  provided  the 
applicant  shows  cause  why  the  additional  power  and  wave 
length  is  desired. 

6.  The  operator  is  required  to  preserve  the  secrecy  of  all 
messages  sent  or  received  upon  the  penalty  of  a  fine  and  im- 
prisonment. 

7.  The  experimenters  must  use  sharp  and  pure  waves. 

8.  The  penalty  for  sending  a  false  message  of  any  kind 
will  be  a  fine  up  to  $1,000  or  imprisonment  up  to  two  years  or 
both.     (Distress  signal,  $2,500—5  years.) 

9.  The  operation  of  wireless  instruments  for  either  send- 
ing or  receiving  except  as  before  stated,  without  a  license,  will 
be  punishable  by  a  fine  of  not  more  than  $500  and  the  forfei- 
ture of  the  apparatus.    This  does  not  apply  to  receiving  appa- 
ratus only. 

These  are  simple,  boiled  down  accounts  of  the  main 
requirements  and  provisions  of  the  law  as  far  as  the 
experimenter  is  concerned.  Information  will  be  fur- 
nished by  the  Secretary  of  Commerce  and  Labor,  without 
expense,  upon  your  request. 

The  licensing  is  free  and  even  advantageous  to  ex- 
perimenters. The  apparatus  described  in  this  book  will 
enable  the  reader  to  comply  with  every  feature  of  the  law 
without  difficulty,  provided  that  the  aerial  used  for  trans- 
mitting purposes  is  not  made  longer  than  70  feet  by 


216  Experimental  Wireless  Stations. 

itself,*  allowing  for  lead-ins  to  make  up  the  remainder  of 
the  effective  length.  The  plan  of  using  a  duplex  aerial 
will  be  found  particularly  valuable  in  accordance  with 
the  law,  so  that  long  distance  messages  may  be  received. 
The  two  aerials  should  be  placed  at  right  angles  to  each 
other  if  possible  in  order  to  avoid  unnecessary  absorp- 
tion of  the  transmitted  energy.  There  is  no  cause  for 
alarm  over  the  new  law. 

The  Department  of  Commerce  and  Labor  has  formed  certain 
rules  and  regulations  which  must  be  adhered  to.  Administra- 
tion districts  have  been  established,  with  offices  at  the  custom- 
houses. Classifications  have  been  made  for  the  purpose  of  ad- 
ministration. Pull  particulars  can  be  obtained  gratis  by  ad- 
dressing the  Commissioner  of  Navigation.  The  first  thing  to  do 
is  to  write  for  forms  No.  756  and  757.  Full  instructions  will  be 
sent  at  the  same  time.  There  will  not  be  any  difficulties  in  ob- 
taining a  license,  but  it  is  imperative  that  you  apply  for  the 
license  at  once. 

PATENTS. 

While  most  of  the  wireless  apparatus  is  covered  more 
or  less  completely  by  patents,  the  experimenter  need  have 
no  concern.  While  the  experimenter  is  legally  an  in- 
fringer  when  he  uses  patented  apparatus  without  per- 
mission from  the  patentee,  it  is  generally  recognized  that 
experimenters  may  use  patented  articles  for  purely  non- 
commercial purposes  without  liability.  This  educational 
idea  seems  to  be  so  fixed  that  even  manufacturers  and 
dealers  in  patented  experimental  goods  not  made  under 
license  or  permission  of  the  patentee,  are  for  the  most 
part  perfectly  safe,  since  the  patent  rights  are  seldom 
pushed  into  this  realm.  The  author  feels  a  little  on  the 
subject  and  certainly  does  not  advise  the  open  and  wilful 
infringement  of  patents,  but  also  believes  that  for  educa- 
tional and  experimental  purposes  where  no  commercial 


This  allows  a  height  of  50  to  70  feet  for  leads,  etc. 


The  Experimenters  Rights.  217 

profits  are  realized  from  such  use,  the  use  of  patented 
articles  is  recognized  as  legitimate  in  effect  if  not  in  the 
legal  sense.  The  readers  need  have  little  concern  on  this 
points  as  long  as  they  do  not  make  or  sell  or  rent  the  appa- 
ratus for  commercial  gain.  Even  then,  if  in  moderation, 
it  is  not  likely  that  there  will  be  any  great  difficulty. 

While  there  is  a  large  field  for  improvement  in  the 
new  art,  the  reader  is  not  advised  to  take  out  or  apply 
for  patents  unless  he  is  sure  that  the  device  has  merit,  is  a 
real  improvement,  and  is  needed,  as  otherwise  failure  in 
one  form  or  another  will  generally  result.  There  are  at 
the  present  time  something  like  1,500  or  2,000  patents  in 
full  force  which  cover  wireless  apparatus  and  systems. 
While  a  part  of  these  are  useless  and  obsolete,  it  is  not 
unlikely  that  the  very  improvement  you  have  in  mind 
is  embodied  in  one  or  more  of  these,  so  that  it  is  well  to 
have  a  search  made  into  the  records  before  spending 
money  for  applications,  models,  etc.  This  is  not  intended 
to  discourage  but  rather  to  encourage  in  the  right  direc- 
tion. The  author  has  treated  the  matter  of  inventions 
and  patents  quite  fully  in  another  volume  which  is  soon 
to  be  published. 

In  conclusion  it  seems  well  to  remark  that  the  present 
tendency  in  the  art  is  toward  the  permanent  establishment 
of  large  chains  of  powerful  land  stations  employing  direc- 
tive aerials,  the  simplification  of  ship,  train,  and  portable 
stations,  the  use  of  long  wave  lengths  for  large  power 
radiation,  the  employment  of  high  pitch  musical  tones  for 
transmission,  the  transmission  methods  which  make  re- 
ception inaudible  except  when  the  principle  of  beats  is 
employed  at  the  receiving  station,  the  use  of  amplifiers  to 
increase  the  effective  intensity  of  the  received  energy, 
and  a  beginning  toward  early  standardization.  Among 
the  new  developments  some  brief  mention  of  the  Edel- 


218  Experimental  Wireless  Stations. 

man  Differential  Wave  System  will  doubtless  be  of  inter- 
est. Experiments  by  the  author  have  already  shown 
that  all  of  the  common  disturbances — undesired  signals  as 
well  as  atmospherics — do  not  interfere  with  this  system. 
The  promising  experiments  with  pin  point  gaps,  liquid 
transmitters,  stepped-up-frequency-alternators,  and  low 
aerials  also  deserve  to  be  mentioned. 

The  reader  will  do  well  to  continue  with  the  study,  as 
much  interesting  and  useful  material  of  an  advanced  na- 
ture is  to  be  had. 

And  so,  we  come  to  the  end  of  the  book  but,  it  is 
hoped, 

Only  the  Beginning  of  a  Study  of  the  Wonderful  New 

Art. 


WIRELESS  CODES. 


WHEN-Two  are  s/»«i»-lst  i's 

W H  EN-Tfoee  ore  ^en /st  ,s  M»t-setg«fConfin€ntQ»t 


A»«  rv/ 
«••    N 


Philip E  EJelwan. 


Note:    The  Navy  code  has  been  superseded  by  the  Con- 
tinental code,  and  is  no  longer  used. 


TABLE  OF  CONTENTS 


Page 
Foreword.  5 

Chapter    1.    Nature   and   Theory   of   Wireless   Transmission    of      8 
Intelligence. 

Relation  of  Stations  —  Effect  of  Earth  —  Function  of  Aerial 

—  Theories  of  Transmission  — Height  of  Aerial  —  Directive 
Aerials  —  Comparison  to  Wave  Motions  —  Absorption  — 
Effect  of  Distance  —  Definition  and  Comparison  of  Long  and 
Short  Waves  —  Items  which  affect  Transmission  —  Night 
and  Day  Transmission  —  Composition  of  Earth  —  Effect  of 
Daylight  —  Effect  of  Weather  —  Drawbacks  to  Advancement 
of  Art  —  Interferences  —  Tuned  Waves  —  Forced  Oscilla- 
tions —  Static  Disturbances  —  Electrical  Storms  —  Radiant 
Energy. 

Chapter  2.    Aerials.  18 

Definition  of  wave  length  and  waves  —  Comparison  to  light 
waves  —  Principle  of  aerial  —  Forms  —  Dimensions  —  Merits 
of  long  and  short  waves  and  wave  lengths  —  Location  of 
aerial  —  Aerial  supports  —  Makeshift  aerials  —  Natural  sup- 
ports —  Poles  —  Construction  —  Duplex  aerials  —  Dimen- 
sions —  Length  of  aerials  —  Effective  length  —  Length  for 
200  meter  wave  length  —  Increase  of  capacity  to  compensate 
for  short  aerial  —  Arrangement  of  aerial  wires  —  Number  of 
conductors  —  Damping  —  Definition  —  Advantages  of  plural 
conductors  —  Spacing  —  Umbrella  aerial  —  Modified  umbrella 
aerial  —  Directive  aerial  —  Construction  —  Flat  top  aerials 

—  Advantages  —  L  type  —  T  type  —  Directive  and  Loop 
types  —  Lead  ins  —  Constructional  details  —  Insulators  — 
Leads  ins  —  Arrangements  of  aerial  —  Spreaders  —  Assembl- 
ing —  Conductors  —  Joints  —  Size  of  wires  —  Pulleys  and 
ropes  —  Lead  in  wires  —  Poles  —  Bamboo  —  Jointed  wood 

—  Truss  work  —  Iron  pipes  —  Dimensions  —  Guy  wires  — 
Insulation. 

Chapter  3.    Grounds  and  Lighting  Protection.  39 

Importance  of  good  ground  —  Grounds  in  water  —  Imbedded 
grounds  —  Special  forms  —  Chemical  grounds  —  Connections 
to  gas  and  water  pipes  —  Lightning  ground  —  Indirect 
ground  — Makeshifts  —  The  ground  wire  —  Protection  from 
lightning  —  Experiments  with  static  currents  —  An  efficient 
Lightning  Protection. 


Page 
Chapter  4.    General  Features  of  Transmitters.  —  Resonance.  46 

Tuned  transmitters  —  Direct  and  indirect  coupling  —  Nature 
of  transmitting  circuits  —  Vibrations  —  Close  coupled  trans- 
mitter —  Electrical  dimensions  —  The  oscillatory  circuit  — 

—  Adjustment  —  Primary  and  secondary  circuits  —  Degree  of 
coupling  —  Function  of  condenser  —  Spark  gap  —  Inductance 

—  Relation  of  circuits  —  Mutual  inductance  —  Resonance  — 
Definition  —  Adjustments  —  Time  of  vibration  —  Variation 
of  wave  length  —  Resonant  relations  in  antenna  circuit  — 
Varying  wave  lengths  —  Use  of  inductance  and  capacity  — 
Resonance  with  condenser  circuit  —  Beats  —  Inter-dependence 
of  circuits  —  Increasing  or  decreasing  wave  length  with  a 
given  aerial  —  Harmonic  effect  —  Tuning  —  Order  of  adjust- 
ments —  Resistance  —  Surface  conduction  —  Heat  loss  — 
Effect  on  sharp  tuning  —  Sharp  tuning  —  Beats  —  Double 
wave  length  of  transmitter  —  "Pick  me  up  wave"  —  Reson- 
ance curves  —  Interference. 

Chapter  5.    Planning  the  Transmitter.  —  Calculation  of  Wave    67 
length,  Capacity,  and  Circuits. 

Cost  of  station  —  Range  of  transmission  —  Varying  condi- 
tions —  Range  in  daylight  —  Winter  —  Effect  of  storms  — 
Standard  transmission  range  —  Selection  of  apparatus  — 
Spark  coils  and  transformers  —  Types  of  transformers  — 
Wireless  transformers  —  Relation  of  inductances  and  capacity 
for  resonance  —  Amount  of  capacity  necessary  —  Calculation 
of  condenser  capacity  —  Simple  formula  —  Example  —  Effect 
of  frequency  —  Effect  of  Voltage  —  Effect  of  power  —  Volt- 
age used  in  charging  condenser  —  Simplified  calculation  of 
wave  length  —  Meaning  of  formula  and  applications  —  Ex- 
amples —  Capacity  and  Inductance  to  obtain  standard  200 
meter  wave  length  —  Spark  gap  —  Requirements  for  good 
design  —  Antenna  circuit  —  Capacity  of  antenna  wires  —  Ap- 
portionment of  antenna  wires  to  get  length  for  a  given  set  — 
Design  for  aerial  —  No.  of  conductors  necessary  for  given 
power  —  Location  of  station  —  Operating  room. 

Chapter  6.    Transformers  —  Spark  Coils.  81 

Standard  experimental  size  —  Principle  of  transformer  — 
Design  —  The  core  —  Eddy  and  Hysteresis  loss  —  Flux  leak- 
age —  Data  for  transformers  —  100  watt  to  2  K.  W.  —  Con- 
structional details  —  Core  —  Primary  —  Secondary  —  Mag- 
netic leakage  cores  —  Materials  —  Insulation  —  Section 
winder  —  Assembling  —  Mounting  —  Data  for  reactance  coils 

—  Spark  coil  construction  —  Data  for  coils  to  give  %  inch  to 
10  inch  spark  for  wireless  purposes  —  Cores  —  Primary  — 
Secondary  —  Insulation. 

Chapter  7.    Auxiliary  Apparatus.    Keys.    Electrolytic  Interrupter.    93 
Kickback  Prevention.    Aerial  Switches. 

Electrolytic  interrupter  construction  —  Line  protector  — 
Kickbacks  —  Construction  of  triple  preventer  —  Keys  —  Con- 
struction for  a  heavy  key  —  Attachments  to  handle  heavy 


Page 

currents  —  Magnetic  key  —  Magnetic  blowout  key  —  Oil 
contacts  —  Aerial  switches  —  Automatic  aerial  switch  — 
Automatic  switch  for  large  stations  —  Wiring  for  wireless 
stations. 

Chapter  8.    Transmitting  Condensers.  103 

Principle  of  condensers  —  Nature  of  charge  —  Stages  in  the 
charging  - —  Behavior  of  capacity  —  Calculation  (simplified) 
for  capacity  for  a  given  condenser  —  Examples  —  How  to 
make  a,  condenser  with  a  desired  capacity  —  Table  of  capaci- 
ties required  for  spark  coils  —  Standard  condenser  —  Dielec- 
tric table  —  Design  for  condensers  —  Condensers  for  high 
voltages  —  Series  connections  to  increase  puncture  strength 

—  Structural  considerations  —  Materials  —  Details  —  Material 
for  coatings  —  Arrangement  —  Soldering  tin  foil  —  Assembl- 
ing —  Insulating  oils  —  Simple  experimental  condensers  — 
Variable  condenser  —  Connections. 

Chapter  9.    Calculation  of  Inductance,  Construction  of  Helix  and  116 
Oscillation  Transformer.  Standard  Dimensions.  Loading  coils. 
Simple  formula  for  inductances  —  Examples  —  Formula  for 
helix  — Formula  for  flat  coils  —  Mutual  inductance  —  Formula 

—  Standard  helix  —  Construction  —  Inductance  of  standard 
helix  —  Standard  oscillation  transformer  —  Construction  — 
Inductance  in  microhenrys  of  primary  and  secondary  —  Con- 
struction for  loading  coils  —  Size  for  conductors. 

Chapter  10.    Design  and  Construction  of  Spark  Gaps.  125 

Purpose  of  the  gap  —  Design  —  Size  of  electrodes  —  Length 
of  gap  —  Construction  of  gap  —  Flanges  —  Construction  of 
series  gaps  —  Construction  of  a  rotary  spark  gap  —  Advan- 
tages of  rapid  spark  rate  —  Simple  experimental  rotary  gap  — 
Simple  gaps  —  Compressed  gas  gaps  —  Care  —  Adjustment. 

Chapter  11.    Radiation  Indicators.    Hot  Wire  Ammeter.    Shunt  133 
Resonator.    Wave  Meter. 

Definition  —  Function  of  indicators  —  Uses  —  Wave  meter 

—  Construction  and  use  —  Hot  wire  ammeter  —  Principal  and 
use  —  Tuning  with  meter  as  indicator  —  Construction  of  hot 
wire  ammeter  —  Advantages  —  Construction  and  operation 
of  a  shunt  resonator  —  Cost  of  apparatus  —  Measurements. 

Chapter  12.     Continuous  Waves.   Wireless  Telephone.    Quenched  145 
Spark.    High  Frequency  Alternators. 

A  simple  arc  system  for  telegraphy  and  telephony  —  Design 
and  construction  —  Operation  —  How  to  make  a  Lepel 
quenched  arc  set  (sparkless  system)  —  The  Telefunken 
Quenched  Gap  —  Theory  and  advantages  of  the  quenched 
spark  —  Goldschmidt,  Galletti  and  Telefunken  Alternators. 

Chapter  13.    The  Receiving  Station.  156 

Simple  receiving  apparatus  —  Function  of  the  parts  — Record- 
ing apparatus  —  Telephone  receiver  for  wireless  receiving  — 


Page 

Effect  of  frequency  —  Why  a  detector  is  essential  —  Sensi- 
tiveness of  instruments  —  The  received  signal  —  Energy  re- 
quired —  Energy  received  —  Table  of  sensitiveness  for 
detectors  —  Tuning  —  Requirements  for  the  receiving  station. 

Chapter  14.    Detectors.    Solid  Rectifiers.  161 

Standard  detectors  —  Forms  of  detectors  —  Composition  of 
solid  rectifiers  —  Action  of  rectifiers  —  List  of  sensitive  min- 
erals and  materials  for  detectors  —  Use  of  crystal  —  Mount- 
ings —  Most  popular  detector  —  Pericon  detector  —  Univer- 
sal detector  —  Constructional  details  —  Materials  —  Silicon 

—  Carborundum  —  Galena  —  Molybdenite  —  Iron  pyrites  — 
Selection  of  minerals  —  Patented  detectors  —  Crystal  mount- 
ing —  Solder  for  crystals  —  Substitute  for  solder  —  Size  of 
crystal  —  Pericon  sets  —  Requisites  for  universal  detector  — 
Points  for  detectors  —  Mechanical  movements  and  adjust- 
ments —  Clamp  and  multipoint  types  —  Care  and  adjustment 

—  Renewing  crystals  —  Buzzer  test  —  Contact  experiment. 

Chapter    15.    Telephone    Receivers.     Detectors    for    Continuous  172 
Waves.    Einthoven  Galvanometer.    Measuring  the  Intensity 
of  Signals. 

Theory,  construction  and  operation  of  an  Einthoven  Galvano- 
meter —  Sensitiveness  of  the  galvanometer  —  Principle  and 
construction  of  choppers  for  receiving  circuits  —  Receivers 
for  arc  system  —  Telephone  receivers  —  Requisites  —  Advan- 
tages of  a  single  receiver  —  Why  ordinary  low  resistance 
telephone  receivers  are. not  suitable  —  Rewound  receivers  — 
Diaphrams  for  wireless  purposes  —  What  the  resistance  really 
means  —  Desirable  resistance  —  Care  and  adjustment  —  Test 
for  magnetism  —  Standard  receivers  —  Advantages  of  conse- 
quent pole  type  —  Size  of  wire  —  Size  of  diaphram  —  How 
the  receiver  operates  —  Measuring  the  intensity  of  received 
signals. 

Chapter  16.    Tuning.    Interference  Prevention.  181 

Similarity  of  transmitting  and  receiving  circuits  —  Resistance 
of  detector  —  Why  absolute  tuning  is  not  possible  —  Effect  of 
locality  —  Disadvantage  of  close  tuning  —  Requirements  for 
receiving  set  —  Ideal  arrangement  —  Importance  of  tuning  — 
Elaborate  circuits  —  Interference  —  What  interference  is  — 
Natural  and  artificial  interference  —  Remedies  for  natural 
disturbances  —  Hook-ups  —  What  tuning  means  —  Factors  in 
tuning  —  Adjustments  —  Short  and  long  waves  —  Detuning 

—  In-tuning  —  Advantages  of  lopped  aerial  —  Differential  and 
Bridge  methods  —  Tuning  circuits  —  Simple  tuned  circuit  — 
Variable   tuned    circuits — Closed   circuits  —   Variable   coupl- 
ing —  Three  slide  tuner  —  Bridge  system  of  interference  pre- 
vention —  Loose  coupler  —  Theory  and  operation  of  loose 
coupler  —  Tuning  with  the  loose  coupler  —  Series  inductance 

—  Increasing  the  wave  length  —  Decreasing  the  wave  length 

—  Fessenden  Differential  system  of  interference  prevention  — 
Circuit  and  operation  —  Loop  aerial  connection. 


Page 

Chapter  17.    Construction  of  Receiving  Condensers.    Fixed  and  193 
Variable. 

Requirements  for  receiving  condensers  —  Dielectric  materials 

—  Calculation  for  condensers  —  Variable  step  arrangement  — 
Parallel  arrangement  —  Determination  of  proper  capacity  for 
receiving  circuit  —  Construction  of  fixed  condensers  —  Uses 
of  fixed  condensers  —  Substitute  for  large  variable  condenser 

—  Construction  of  units  —  Testing  —  Korda  air  condensers 
— •  Construction  of  the  variable  condenser  —  Rotary  plates  — 
Fixed  plates  —  Assembling  —  Mounting  —  Simple  variable 
condensers  —  Capacity  of  variable  condensers  —  Calculation. 

Chapter  18.    Construction  of  Tuning  Inductances.    Loose  Coup-  202 
ler.    Variometers.    Tuners. 

General  requirements  —  Materials  —  Insulation  —  Wires  — 
Importance  of  insulation  —  Construction  of  slide  type  tuners 

—  Cores  —  The  windings  —  Spacing  wires  —  Core  ends  — • 
Base  —  Sliders  —  Requirements  —  Construction  —  Slider 
rods  —  Loading  coils  —  Standard  tuner  —  Construction  and 
operation  of  a  Variometer  —  Construction  of  a  loose  coupler 

—  Primary  —  Core  —  Heads  for  primary  —  Base  —  Secondary 

—  Slider  —  Mountings  —  Couplers  for  differential  circuit  — 
Condenser  for  differential  circuit  —  Pancake  type  —  Uses  for 
the  several  types. 

Chapter  19.     Conclusion.    The  Rights  of  the  Experimenter.  213 

Arrangement  of  apparatus  —  Connections  —  Field  for  experi- 
ments —  The  new  wireless  law  —  What  it  means  to  the  ex- 
perimenter —  Its  effect  —  Letter  from  the  Commissioner  of 
Navigation  —  Restrictions  —  Licenses  —  Power  —  Wave 
length  —  Inter-state  transmission  —  Receiving  Stations  — 
Secrecy  of  messages  —  Sharp  and  pure  waves  —  Penalties  — 

—  Fines  —  How  to  comply  with  the  law  —  Advantages  of  the 
duplex  aerial  and  standard  designs  under  the  new  law  —  Pat- 
ents —  Concerning  infringement  —  Liability  to  prosecution  — 
Field  for  improvements  —  Taking  out  patents  —  Number  of 
wireless  patents  in  force  —  Learning  the  codes  —  Studying 
the  art. 

Wireless  Codes,  Morse,  Continental,  and  Navy.  219 


1916  SUPPLEMENT. 

AUTHOR'S  NOTE. — Previous  editions  of  Experimental  Wire- 
less Stations  have  been  distributed  to  and  welcomed  in  all  parts 
of  the  world.  Thousands  of  readers  have  been  kind  enough  to 
say  that  they  have  gained  much  from  the  book.  Many,  indeed, 
have  voluntarily  sent  photographs  and  descriptions  of  their  suc- 
cess after  following  the  directions.  The  book  has  won  on  its 
merits  and  has  attained  a  wide  influence. 

The  radio  art  is  still  in  the  process  of  evolution.  Experi- 
mental work  continues  to  keep  well  ahead  of  commercial 
practice.  What  appears  wonderfully  important  today  may  be 
of  only  historical  interest  tomorrow.  Still  the  fundamental 
principles  remain.  Behind  the  novel  forms  of  commercial  ap- 
paratus continually  brought  out  and  inside  of  the  nicely  polished 
boxes  you  will  find  the  same  coils,  condensers  and  simple  appa- 
ratus described  in  this  book. 

The  present  supplement  aims  to  append  notes  which  will 
bring  the  book  right  up  to  the  present  time.  Much  of  the 
material  here  presented  has  not  been  published  before  in  any 
form.  Attention  is  called  to  the  patent  index,  which  demanded 
considerable  expense  and  labor  from  the  author.  It  should, 
however,  save  the  readers  much  time  and  money.  Copies  of  the 
patents  may  be  found  in  all  large  public  libraries  or  can  be 
purchased  for  5  cents  each.  They  are  the  key  to  the  art,  and 
often  a  single  paper  will  contain  all  that  is  known  about  a  par. 
ticular  subject. 


CONTENTS. 


RAILROAD    WIRELESS 
AUTOMOBILE  WIRELESS 
AEROPLANE    WIRELESS 
WIRELESS   COMPASS 
TELEMECHANICS 
BALANCING  AERIALS 
GROUND   AERIALS 
RADIATION  RESISTANCE 
HETERODYNE    RECEIVER 
VACUUM   VALVES 
AUDION 
PLIOTRON 
AMPLIFIERS 


ULTRA  AUDION 
AUDION   GENERATOR 
TRANSCONTINENTAL   WIRE- 
LESS TELEPHONE 
LONG  WAVE  STATIONS 
LONG    WAVE    TUNERS 
TIME   SIGNALS 
WEATHER   SIGNAL    CODE 
U.    S.    WIRELESS    PATENTS 
(Most     complete    list    issued 
from    the    beginning    to    the 
present) 
MISCELLANEOUS  NOTES 


Copyright  1916  by  Philip  E.   Edelman.    All  rights  reserved. 


1916  SUPPLEMENT. 


RAILROAD  WIRELESS. 

Railroad  wireless  telegraphy  and  telephony  differs  in 
no  way  from  radiocommunication  for  other  purposes 
except  that  the  aerial  consists  of  two  or  three  wires 
suspended  just  a  little  above  the  train  car  while  the 
ground  is  through  the  trucks  to  the  rails.  Couplings 
are  provided  for  the  aerial  between  cars.  The  Delaware 
and  Lackawanna  Railroad  has  had  much  success  with 
such  moving  stations  in  conjunction  with  a  few  fixed 
land  stations  and  communication  is  regularly  established 
with  the  moving  trains  both  ways,  even  when  the  train  is 
passing  through  a  tunnel. 

AUTOMOBILE  WIRELESS. 

Successful  communication  may  be  established  over 
several  miles  with  a  small  wireless  station  on  an  auto- 
mobile, using  a  small  aerial  suspended  a  few  feet  above 
or  within  the  top  and  using  the  metal  body  of  the  car 
as  a  counterbalance  in  lieu  of  a  ground.  For  army  use, 
the  automobile  is  merely  used  to  transport  and  contain 
the  apparatus  and  a  portable  aerial  is  rapidly  erected 
when  communication  is  to  be  established. 

AEROPLANE  WIRELESS. 

Wireless  communication  is  successfully  used  on 
aeroplanes  to  communicate  to  military  bases  from  the 
air  or  enemy  territory.  The  apparatus  comprises  a  small 
sending  and  receiving  station  of  light  weight.  The 
receivers  are  provided  with  sound  protectors  but  receiv- 
ing is  less  successful  than  sending  because  of  propeller 


Supplement.  227 


noise.  The  aerial  is  generally  mounted  on  the  planes 
and  a  counterpoise  or  additional  aerial  is  used  instead  of 
a  ground.  Hanging  aerials  from  reels,  etc.,  are  con- 
sidered dangerous  and  obsolete.  The  total  weight  of  the 
equipment  need  not  be  over  50  pounds.  Use  of  the  wire- 
less to  direct  gun  fire  and  report  troop  movements  has 
been  tried  with  some  success. 

WIRELESS  COMPASS. 

The  Bellini  and  Tosi  compass,  of  which  a  very  few 
made  by  the  Marconi  Co.,  are  at  present  in  use,  utilizes  an 
almost  closed  triangular  oscillating  antenna  which  radiates 
and  also  receives  the  strongest  in  its  own  plane  and  the 
least  at  right  angles  thereto.  Two  partially  closed 
looped  aerials  are  placed  at  right  angles  to  each  other 
and  each  is  connected  to  a  primary  of  a  loose  coupler 
having  two  primaries  at  right  angles  to  each  other  and 
a  single  secondary  winding  which  is  rotatable  therein. 
For  any  position  of  this  secondary  winding  the  received 
energy  will  be  proportionately  due  to  the  two  primaries 
so  that  by  observing  when  the  received  signals  are 
strongest  the  sending  station  can  be  located  within  two 
or  three  degrees.  This  is  most  useful  in  foggy  weather. 
For  sending  the  same  arrangement  is  used  with  a  trans- 
mitting oscillator  connected  to  the  two  aerials  in  the 
same  manner  so  that  signals  can  be  sent  out  strongest  in 
a  desired  direction.  International  radio  regulations  re- 
quire such  stations  to  use  small  power  and  low  wave- 
lengths, this  being  necessary  in  order  to  avoid  interfer- 
ence with  other  communications. 

The  set  uses  no  ground  connection  and  is  shown  in 
figure  82.  The  aerials  A,  B,  respectively  are  connected  to 
the  primaries  A',  B',  respectively  of  a  loose  coupler 


228 


Experimental  Wireless  Stations. 


•  7051 


FIG. 


HETERODYNE  RECEIVER 


Supplement.  229 


called  a  goniometer.  The  secondary  S,  wound  on  a 
spherical  core  connects  to  an  ordinary  detector  circuit 
and  is  movable  by  means  on  handle  R  which  carries  a 
pointer  so  that  degrees  may  be  read  on  a  scale  Q.  In 
practice  a  slightly  elaborated  arrangement  is  used.  For 
purposes  of  demonstration  it  is  not  difficult  to  rig  up  an 
outfit  of  this  kind. 

With  the  Telefunken  compass  an  ordinary  antenna 
on  a  ship  may  be  used  in  conjunction  with  shore  sta- 
tions. Thirty-two  separate  aerials  arranged  in  the  form 
of  an  umbrella  are  used  at  the  shore  station  for  sending, 
a  rotatable  switch  being  provided  so  that  each  antenna 
may  be  separately  and  successively  connected  to  the 
sending  apparatus.  Aboard  the  ship  the  direction  is 
determined  by  comparing  signal  strengths.  Various 
other  arrangements  have  also  been  proposed  but  none 
appear  to  have  come  into  use  up  to  the  present  time. 

HETERODYNE  RECEIVER. 

This  receiving  method  originated  by  R.  Fessenden 
permits  the  tone  of  the  received  signals  to  be  varied  at 
will,  thus  aiding  in  overcoming  interference,  and  also 
slightly  increases  the  sensitiveness  of  the  received  sig- 
nals. It  consists  (Fig.  83)  essentially  of  an  ordinary 
receiving  set  which  is  coupled  with  a  local  miniature 
sending  set  such  as  an  arc  or  audion  high  frequency 
oscillator.  If  for  example  the  incoming  signals  have 
a  frequency  of  300,000  and  the  local  oscillator  is  ad- 
justed to  a  frequency  of  300,516  the  interaction  sets  up 
beats  by  interference  which  give  a  musical  tone  of  516 
frequency  in  the  head  receivers.  This  method  is  particu- 
larly useful  for  reception  from  undamped  wave  stations 
but  may  also  be  used  with  spark  oscillations. 


230  Experimental  Wireless  Stations. 

TELEMECHANICS. 

Wireless  controlled  torpedoes,  boats,  fog  guns,  etc., 
have  been  successfully  experimented  with  so  that  ap- 
plications may  be  expected  to  come  into  use  soon.  Most 
of  this  work  has  been  done  with  the  use  of  a  coheror 
receptor  and  various  mechanical  switch  and  tuning  ar- 
rangements. It  is  now  possible,  however,  to  use  the 
more  sensitive  audion  and  amplified  circuits  already 
mentioned  for  this  purpose.  A  simply  made  outfit  for 
demonstrating  the  various  possible  applications  is  de- 
scribed in  chapter  13  of  the  book  "Experiments"  by  the 
author  which  may  be  obtained  for  $1.50.  Reference  to 
the  patent  index  in  this  supplement  will  give  the  reader 
the  key  to  the  results  of  previous  workers  on  this  sub- 
ject. 

BALANCING  AERIALS. 

The  new  Marconi  duplex  stations  are  to  use  a  bal- 
ancing aerial  at  the  receiving  station  to  overcome  inter- 
ference from  the  sending  end  of  the  station  a  number  of 
miles  away  which  is  in  simultaneous  use.  This  is  simply 
an  aerial  placed  at  right  angles  to  the  receiving  aerial 
and  of  lesser  height  which  is  coupled  to  the  main  aerial 
through  a  loose  coupler  in  such  a  way  that  the  energy 
received  by  the  one  aerial  is  neutralized  by  that  received 
by  the  other  from  the  strong  nearby  station.  The  large 
aerial  receives  the  long  distance  signals  as  usual  but  the 
balancing  aerial  being  both  lower  and  at  right  angles 
does  not  receive  enough  energy  from  the  distant  station 
to  deter  the  reception  of  signals  therefrom.  A  single 
horizontal  wire  suffices  for  the  balancing  aerial. 


Supplement.  231 


GROUND  AERIALS. 

Experiments  with  grounded  aerials  show  that  sig- 
nals may  be  received  for  distances  of  at  least  3,000  miles 
with  an  ordinary  receiving  set  by  simply  using  a  bare 
or  insulated  wire  spread  upon  or  supported  a  few  feet 
above  the  ground  as  an  aerial  with  a  counterpoise.  A 
single  wire  has  been  found  to  be  the  best  especially  if  a 
Y  is  connected  to  its  ends  and  such  an  antenna  has  also 
been  found  to  be  directive.  The  counterpoise  is  best 
made  exactly  like  the  aerial  and  arranged  opposite  it  so 
that  the  receiving  set  is  at  the  middle  of  a  symmetrically 
placed  conductor  adjacent  to  the  ground.  For  sending 
purposes  such  an  arrangement  has  not  been  found  ef- 
fective except  over  a  short  distance. 

RADIATION  RESISTANCE. 

This  term  originated  with  J.  S.  Stone  and  means  the 
equivalent  resistance  which  would  consume  the  same 
energy  as  that  withdrawn  from  the  sending  antenna  by 
radiation.  It  is  often  used  and  according  to  R.  Rueden- 
berg  is  approximately  equal  to 

1,600  (height  from  earth  to  center  of  capacity  of  antenna)2 

(wave   length)2 
ohms,  the  meter  being  the  unit  of  length. 

VACUUM  VALVES-AMPLIFIERS,  DETECTORS, 
AND  OSCILLATORS. 

Recently  vacuum  valves  have  come  into  general  use 
for  detecting  and  amplifying  signals.  There  are  several 
types  of  these  bulbs,  all  of  which  depend  substantially  on 


Experimental  Wireless  Stations. 


the  same  operating  principles,  the  difference  being  in 
the  details  of  construction  and  degree  of  vacuum  em- 
ployed. 

FLEMING  VALVE. 

The  Fleming  valve,  one  of  the  first  of  these,  consists 
simply  of  a  miniature  electric  light  bulb  with  a  filament 
and  a  metal  plate  near  it  as  shown  in  fig.  84.  In  use, 


FIG  66. 


current  may  pass  from  the  filament  to  the  plate  but  not 
reversely  so  that  the  device  acts  as  a  rectifier.  It  is  not 
very  sensitive  and  relatively  few  are  in  use  now.  The 
kenotron  is  a  similar  device  which  is  evacuated  so  that 
less  gas  is  left  in  the  bulb.  The  kenotron  is  very  highly 
evacuated  and  built  for  larger  current  but  is  not  used 
for  wireless  purposes  at  present. 


Supplement. 


233 


AUDION. 

The  audion  (fig.  89)  is  like  the  previously  described 
device  except  that  a  grid,  which  is  simply  a  piece  of  bent 
wire  or  metal  screen  or  plate  with  holes,  is  placed  be- 


tween  the  filament  and  the  metal  plate  or  wing.  The 
audion  has  a  double  filament,  only  one  filament  of  which 
is  heated  at  a  time,  the  other  being  saved  for  use  when 
the  first  burns  out.  This  filament  is  usually  connected 
to  a  6  volt  storage  battery  through  a  small  rheostat. 


234  Experimental  Wireless  Stations. 

Separated  from  the  filament  by  about  J^  inch  is  the  plate 
and  between  the  two  at  the  middle  and  insulated  from 
both  is  the  grid.  The  plate  is  about  %  inch  square  and 
of  sheet  nickel  in  the  size  used  as  a  detector.  The  whole 
is  sealed  in  a  glass  bulb  and  evacuated  so  that  only  a 
little  gas  is  left.  Various  other  forms  have  been  made 
with  two  plates  and  grids,  in  larger  sizes,  with  cylind- 
rical plates,  etc.,  but  the  principle  of  operation  is  the 
same  in  all  types.  The  device  called  the  pliotron  is 
similar  in  all  respects  except  that  the  bulb  is  very  highly 
evacuated.  Experimental  bulbs  have  also  been  made 
in  which  mercury  vapor  is  introduced  into  the  bulb  after 
it  has  been  evacuated. 

LIEBEN-REISZ  AMPLIFIER. 

The  Reisz  gas  tube  as  described  in  U.  S.  patent 
1,142,625  is  shown  in  fig.  85.  The  circuit  in  which  it 
is  used  is  given  in  fig.  86.  T1  and  T2  are  iron  core  step 
up  transformers.  The  device  is  analogous  to  the  audion 
which  is  better  known  and  will  be  understood  from  dis- 
cussions of  the  latter  device. 

PLIOTRON.     CASCADE  AMPLIFIER. 

This  device  has  two  plates,  a  grid  of  fine  wire 
wrapped  around  a  support  F  (fig.  87)  and  a  filament 
held  in  this  support.  It  is  very  highly  evacuated  so  that 
much  higher  voltages  must  be  used  with  it  than  in  the 
case  of  the  audion.  It  can  be  built  in  larger  sizes  than 
the  audion  for  use  as  an  undamped  wave  generator  or 
relay  and  is  more  constant,  so  that  whereas  audions  vary 
widely  in  characteristics,  these  more  highly  evacuated 
bulbs  are  nearly  identical  and  many  of  them  may  be  con- 


Supplement. 


235 


nected  in  parallel.  Two  such  devices  connected  in 
cascade  for  receiving  radio  signals  with  an  amplifica- 
tion as  high  as  1,000  times  are  shown  in  fig.  88.  L1 
and  L2  are  the  primary  and  secondary  of  an  air  core 


PL/ or fto  N 


CASCADE    HAO/O 


transformer.  The  first  bulb  detects  and  amplifies  the 
incoming  oscillations  and  the  second  bulb  again  amplifies 
the  previously  amplified  oscillations.  The  battery  B' 
must  afford  several  hundred  volts  and  the  battery  B" 
is  required  to  charge  the  grid.  A  similar  circuit  may  be 
used  with  ordinary  audion  bulbs  except  that  batteries  B ' ' 
arc  not  required. 


236  Experimental  Wireless  Stations. 

PRINCIPLE  OF  OPERATION. 

It  should  be  remembered  that  there  are  two  distinct 
actions  of  this  class  of  valves,  the  one  holding  for  bulbs 
containing  appreciable  gas  so  that  ionization  can  occur 
by  collision  and  the  other  taking  place  in  bulbs  so  highly 
evacuated  as  to  be  almost  free  from  gas  so  that  a  purely 
electronic  action  occurs.  The  first  class  of  bulbs  may  be 
recognized  by  the  blue  glow  which  occurs  just  beyond 
the  sensitive  and  operating  adjustment  as  in  the  audion. 
The  Lieben-Reisz,  Audio-tron  and  similar  tubes  are  also 
of  the  first  class.  The  second  class  embraces  bulbs  such 
as  the  pliotron  in  which  a  pure  electron  discharge  occurs 
from  the  heated  cathode  or  filament.  The  second  class 
does  not  rely  upon  residual  gas  as  a  conducting  medium 
as  in  devices  of  the  first  class. 

The  hot  filament  in  these  devices  emits  electrons.  In 
elementary  static  electricity  it  will  be  remembered  that 
like  charges  repel  and  unlike  attract;  negative  repels 
negative  for  instance.  The  electron  may  be  considered 
as  the  smallest  possible  particle  of  electricity,  the  atom 
of  electricity  so  to  speak,  and  furthermore  it  is  always 
negative.  Hence  if  an  electron  comes  near  a  negative 
charge  or  a  piece  of  metal  charged  negatively  by  a  bat- 
tery the  electron  will  be  repelled,  or  on  the  other  hand 
the  same  piece  of  metal  if  charged  positively  will  at- 
tract the  electron  to  it. 

Now  in  a  highly  evacuated  bulb  containing  filament, 
grid,  and  plate,  the  resistance  between  the  filament  and 
grid  or  plate  when  the  filament  is  cold  is  very  high,  and 
a  pressure  of  100  volts  for  example  can  send  no  current 
across  such  a  path.  As  soon  as  the  filament  is  heated, 
however,  electrons  are  emitted  from  the  hot  cathode  and 


Supplement.  237 


fill  the  surrounding  space.  As  soon  as  the  space  is  filled, 
however,  additional  electrons  which  are  emitted  by  the 
filament  cathode  are  repelled  by  the  electrons  already 
in  the  space  and  are  absorbed  again  by  the  cathode.  If 
now  the  grid,  which  is  between  the  plate  and  the  fila- 
ment is  negatively  charged  by  a  battery  still  more  elec- 
trons will  be  repelled  and  sent  back  to  the  filament,  but 
on  the  other  hand  if  this  grid  is  positively  charged  the 
electrons  will  be  attracted  to  it  and  a  larger  current  will 
flow  from  the  filament.  This  is  the  case  for  the  pliotron. 

When,  however,  there  is  gas  present,  as  in  the  audion, 
the  electrons  in  passing  from  the  filament  to  the  plate 
ionize  the  gas,  that  is  split  it  up  into  elementary  parts 
carrying  electric  charges  so  that  the  gas  becomes  a 
conductor.  Now  some  of  the  charges  of  the  ionized  gas 
are  positive  and  these  partly  neutralize  the  electrons 
which  have  been  projected  into  the  space  by  the  filament. 
Also  if  a  positive  charge  is  applied  to  the  grid  the  elec- 
trons from  the  filament  will  be  attracted  and  pass  more 
rapidly.  In  so  doing  they  produce  more  ions  in  the  gas 
and  the  action  continues — more  electrons  pass  the  grid 
and  more  ionization  takes  place.  Now  every  time  ioniza- 
tion  occurs  or  increases  the  electrons  in  the  space  are 
reduced  so  that  a  much  larger  current  can  flow  from  the 
filament.  Only  a  small  amount  of  gas  need  be  present 
for  this  purpose.  In  fact  if  too  much  gas  is  present 
there  will  be  too  much  ionization  and  too  large  a  current 
will  flow  giving  a  blue  glow  and  spoiling  the  relaying 
effect. 

On  such  a  basis  we  can  understand  what  happens  in 
the  tube.  Fig.  89  shows  the  ordinary  audion  circuit. 
Both  detection  as  in  a  crystal  rectifier  and  amplification 
of  the  received  energy  by  trigger  action  occur.  In  use 


238  Experimental  Wireless  Stations. 

the  filament  is  brought  to  incandescence  and  tuning  ad- 
justments are  made  until  the  desired  signals  are  brought 
in.  The  incoming  signals  are  embodied  in  oscillations 
and  these  are  rectified  between  the  filament  and  grid. 
One-half  cycle  passes,  the  other  cannot  because  the  hot 
filament — cold  grid  is  uni-directional.  In  the  Fleming 
valve  this  is  all,  but  in  the  audion  under  consideration 
amplification  now  occurs.  The  battery  B2  causes  current 
to  pass  from  the  plate  to  the  filament  but  by  the  action 
already  explained  the  negatively  charged  grid  decreases 
it.  When  this  current  decreases  the  change  registers 
on  the  head  phones  and  a  loud  response  results  which 
is  much  stronger  than  would  result  from  the  rectification 
alone.  The  potential  on  the  grid  caused  by  the  incoming 
oscillations  controls  the  larger  current  passing  from  the 
plate  to  the  filament  and  through  the  phones  to  give  the 
signal.  A  small  increase  of  the  potential  on  the  grid 
means  in  practice  a  large  change  in  the  current  passing 
between  the  grid  and  filament,  and  this  in  turn  causes  a 
corresponding  change  in  the  current  passing  through  the 
phones  by  way  of  the  plate  to  filament  circuit. 

This  device  generally  works  best  just  below  the  point 
which  causes  a  blue  glow  to  appear.  The  filament  should 
not  be  lighted  when  the  set  is  not  in  use  because  this  re- 
sults in  a  waste  of  current  from  the  high  voltage  battery 
and  deteriorates  the  filament.  When  the  filament  is 
lighted  and  the  device  is  ready  to  use,  the  high  voltage 
battery  causes  a  continual  flow  of  current  through  the 
bulb:  the  incoming  oscillations  merely  cause  this  current 
to  vary. 

EFFECT  OF  MAGNET  ON  AUDION. 

If  a  magnet,  permanent  or  electromagnet,  is  brought 
near  an  audion  in  operation  various  effects  may  be  pro- 


Supplement.  239 


duced.  Sometimes  this  merely  causes  the  blue  glow  to 
appear.  In  other  cases  the  bulb  starts  to  send  pulsations 
through  the  phones  at  a  rate  which  gives  musical  tones 
which  may  be  made  to  run  all  the  way  up  and  down  the 
scale  by  proper  motion  of  the  magnet.  If,  however,  the 
magnet  is  brought  in  the  proper  plane  the  thermionic 
stream  can  be  concentrated  so  that  in  very  many  cases 
the  bulb  will  work  better  than  ever  and  give  an  increased 
amplification.  This  may  be  quickly  found  by  trial. 

THE  ULTRA-AUDION  RECEIVER. 

De  Forests'  ultra-audion  is  a  form  of  heterodyne 
circuit  combined  in  one  instrument.  It  is  an  ordinary 
audion  detector  with  a  receiving  circuit  (fig.  90)  in 
which  the  inductance  L  is  large  (secondary  of  loose 
coupler  wound  with  many  turns  of  No.  30  to  36  wire) 
while  the  condenser  C'  is  only  about  .0002  microfarad 
in  capacity.  The  condenser  VC  is  also  made  small.  The 
electron  flow  in  the  audion  used  in  this  circuit  is  auto- 
matically unbalanced  because  of  this  system  of  induc- 
tance and  capacity  so  that  continuous  oscillations  are  set 
up.  These  oscillations  are  strengthened  by  the  variable 
condenser  C".  Any  audion  bulb  may  be  connected  up 
in  this  manner  to  receive  undamped  wave  signals,  for 
when  the  capacities  are  adjusted  so  that  the  audion  sets 
up  oscillations  slightly  differing  in  frequency  from  those 
received,  beats  result  which  are  heard  in  the  head  re- 
ceivers. 

Often  an  ordinary  audion  in  a  common  receiving  set 
will  oscillate  in  such  manner  if  only  the  filament  is 
burned  slightly  brighter  than  usual.  One  may  ascertain 
that  the  bulb  is  oscillating  by  touching  any  portion  of  the 
metallic  circuit  between  L  and  C'  whereupon  a  sound 


240 


Experimental  Wireless  Stations. 


will  be  heard  in  the  telephone  receivers  if  the  bulb  is 
oscillating.  For  receiving  from  spark  stations  the  bulb 
is  often  best  when  in  the  non-oscillating  condition  as 
when  oscillating  in  the  above  manner  the  musical  tone 


40 

is 

'o 
<o 

I 


^n 


T/=?A    AUDI  ON      F/6*  SO. 


-^m^ 

Microphone  I- 

^       AUDI  ON 


of  the  sending  spark  becomes  ragged  so  that  a  louder 
but  indistinct  sound  results.  This  is  perhaps  the  most 
sensitive  arrangement  for  detection  which  is  at  present 
available  as  it  affords  a  combined  detector  and  amplifier 
as  well  as  a  local  oscillator. 


Supplement.  241 


AUDION  AS  UNDAMPED  WAVE  GENERATOR. 

A  suitable  circuit  for  obtaining  undamped  waves 
from  an  audion  bulb  is  shown  in  fig.  95.  A  microphone 
may  be  employed  as  shown  so  that  for  demonstration 
purposes  the  arrangement  shown  may  serve  as  a  wire- 
less telephone  transmitter  for  some  little  distance.  The 
filament  of  a  bulb  intended  for  a  detector  will,  however, 
rapidly  waste  away,  so  it  is  best  to  obtain  a  bulb  con- 
structed for  this  purpose.  Any  frequency  can  be  ob- 
tained over  a  wide  range  by  adjustments  of  the  con- 
denser capacity. 

ARMSTRONG  CIRCUIT. 

The  Armstrong  circuit  combines  the  principle  of  the 
singing  microphone  with  the  audion  so  that  a  part  of  the 
amplified  current  reacts  on  the  current  between  the  grid 
and  filament  and  thus  causes  a  still  further  amplification. 
This  is  best  accomplished  by  means  of  a  coupling  coil 
built  like  a  loose  coupler.  If  this  coil  is  made  with  an 
air  core  (no  iron)  the  radio  frequency  oscillations  will 
be  amplified.  Similarly  by  the  use  of  an  iron  core  in- 
duction coil  the  audio  frequency  current  through  the 
telephone  will  be  amplified.  It  is  possible  to  amplify 
either  or  both  at  the  same  time.  In  fig.  91  the  complete 
circuit  for  a  long  wave  set  using  the  oscillating  and 
amplifying  audion  is  given.  Either  spark  or  undamped 
wave  sets  can  be  heard  with  this  arrangement.  A  less 
complicated  circuit  which  will  serve  about  as  well  is 
shown  in  fig.  92.  Compare  with  the  ultra-audion,  fig.  90. 


242  Experimental  Wireless  Stations. 

CONSTRUCTION.      LONG    WAVE    UNDAMPED 
WAVE  RECEPTOR.     RANGE  14,000  METERS. 

Few  of  the  readers  have  the  facilities  to  construct 
the  bulbs,  but  if  one  has  a  bulb  the  amplifying  circuit  may 
be  readily  made  at  small  cost.  When  properly  adjusted 
a  single  bulb  amplifier  of  this  type  is  as  good  or  better 
than  the  usual  two  step  amplifier  employing  two  bulbs. 

The  values  of  the  condenser  capacities  and  maximum 
battery  voltages  are  given  in  the  diagram  of  fig.  91.  The 
inductances  are  made  by  winding  a  single  layer  of  silk 
covered  wire  on  paper  tubes  and  for  the  various  coils 
suitable  dimensions  follow. 

L1 ;  core  6"  diameter  by  25"  long  wound  with  No.  24 
S.  C.  C.  wire,  with  taps  taken  at  ten,  five,  and  then  every 
inch  of  length. 

Loose  coupler  L2,  L3.  Primary  L2;  12"  long  by  6" 
diameter  with  No.  24  S.  C.  C.  Secondary  L3 ;  12"  long 
by  5%"  diameter  wound  with  No.  32  S.  C.  C. 

L4  and  L5  are  each  5"  in  diameter  and  30"  long,  and 
wound  full  of  No.  32  S.  C.  C.  Taps  are  taken  every 
inch  at  the  last  5  inches. 

Loose  coupler  L7,  L6.  L7  is  8"  long  by  5"  diameter. 
L6  is  7%"  long  by  4^"  diameter.  Both  cores  are  wound 
full  of  No.  30  S.  C.  C.  wire. 

The  condensers  should  be  of  the  rotary  plate  type 
and  C2  which  is  used  at  very  small  values  should  have  a 
streak  of  graphite  rubbed  between  its  binding  posts  to 
serve  as  a  high  resistance  shunt  which  dissipates  high 
voltage  accumulations  on  the  condenser  from  static  dis- 
turbances. 


Supplement.  243 


ADJUSTMENT. 

Short  circuit  L5  and  place  C3  at  its  maximum  capa- 
city. Have  L2,  L3  all  in  and  vary  L*  and  the  other  con- 
densers, also  L1  until  the  signals  are  brought  in  best. 
Now  place  L5  in  and  adjust  the  number  of  turns  used  as 
well  as  C3  until  the  loudest  signal  strength  is  obtained. 
Mark  the  adjustments  for  future  reference  and  make 
any  other  necessary  changes  by  means  of  L1,  L2,  L3,  C3, 
and  C1.  When  the  bulb  is  replaced  with  a  new  one,  the 
adjustments  may  have  to  be  repeated  as  new  valves  will 
be  required.  If  siren  effects  bother,  ground  one  terminal 
of  battery  B. 

Fig.  92  will  now  be  readily  understood.  The  loose 
coupler  L2,  L3  is  made  with  variable  coupling,  L2  is  5" 
in  diameter  by  4%"  long.  L3  is  4%"  m  diameter  by 
5"  long.  Both  cores  are  wound  full  of  No.  28  S.  C.  C. 
B2  should  be  adjustable  up  to  40  volts.  The  range  will 
depend  on  the  loose  coupler  used  between  the  aerial  and 
detecting  circuit  and  is  more  suited  to  wave  lengths  under 
6,000  meters. 

CASCADE  CIRCUITS. 

Audions  may  also  be  used  in  cascade  to  amplify 
either  the  audio  or  radio  frequency  currents.  Pliotrons 
can  also  be  used  in  a  similar  manner.  There  is  a  limit 
to  the  number  of  steps  that  can  be  used,  however,  as  the 
amplified  current  soon  causes  distortion,  so  in  practice 
not  more  than  three  bulbs  in  cascade  have  been  found 
to  be  practicable.  In  the  cascade  circuits  it  will  be  noted 
that  the  first  step  is  the  familiar  circuit  while  the  ampli- 
fied current  of  this  step  (at  audio  frequency  in  the  audion 
arrangement)  operates  the  grid  filament  circuit  of  the 


244  Experimental  Wireless  Stations. 

next  step  through  an  iron  core  inductive  coupling;  then 
this  is  repeated  in  the  next  step  in  the  same  manner. 
The  final  current  may  be  large  enough  to  operate  a  loud 
speaking  telephone  or  even  a  relay  or  milliameter. 
Often  signals  with  any  of  the  audion  circuits  have  been 
so  loud  that  they  could  be  directly  recorded  on  a  wax 
cylinder  phonograph  by  simply  holding  the  telephone 
receiver  against  the  recording  diaphram. 

CASCADE  CIRCUIT  CONSTRUCTION. 

Fig.  93  shows  how  to  connect  two  ordinary  audion 
bulbs  in  cascade  to  amplify  the  audio  frequency.  Com- 
pare with  fig.  88  and  note  that  these  two  figures  could 
be  combined  to  still  further  increase  the  magnification. 
The  transformer  consists  of  a  core  i"  in  diameter  and  10" 
long  made  up  of  a  bundle  of  soft  iron  wires  wound  with 
tape.  The  primary  winding  consists  of  one  pound  of 
No.  36  S.  S.  C.  wire.  Over  this  the  secondary  of  one 
and  one-half  pounds  No.  36  S.  C.  C.  wire  is  wound. 
Amplification  up  to  about  100  may  be  expected. 

DISADVANTAGES  OF  AUDION.    COMPARISON 
WITH  CRYSTAL  DETECTOR. 

The  audion  detector  as  now  sold  is  bulky,  fragile, 
and  requires  frequent  care  and  renewal  of  batteries,  bulb, 
etc.  Many  bulbs  are  not  constant  and  some  give  annoy- 
ing siren  effects.  In  very  many  cases  there  really  is  no 
need  to  employ  any  such  device  for  a  crystal  detector 
will  do  as  well  or  better.  A  well  adjusted  crystal  de- 
tector is  very  nearly  as  sensitive  as  the  best  audion  de- 
tector and  will  bring  in  most  if  not  all  the  stations  that 
an  audion  will.  A  crystal  detector  such  as  galena  will 


Supplement. 


245 


even  detect  signals  from  arc  and  undamped  wave  sets 
under  favorable  conditions  and  the  author  has  heard 
such  signals  when  using  such  a  detector  in  a  receiving 
circuit  containing  a  variometer  coupler  which  caused  the 
necessary  reaction  in  the  circuits.  The  tone,  however, 
was  not  musical. 

The  audion  as  an  amplifier,  is  superior,  as  the  usual 
received  signals  are  amplified  to  advantage.     Indeed  the 


FIG  94. 


6    r 


audion  may  be  combined  with  a  good  crystal  detector  to 
advantage,  the  one  rectifying,  the  other  amplifying  the 
rectified  current. 

AUDION  WITH  CRYSTAL  DETECTOR. 

The  connections  for  using  an  audion  with  a  crystal 
detector  such  as  galena  are  shown  in  fig.  94  and  afford 
an  amplification  of  about  10  times  the  signal  strength 
obtained  with  the  detector  alone. 

OTHER  AMPLIFIERS. 

Brown's  microphone  relay  has  found  slight  use.  It 
is  connected  in  place  of  the  phones  and  amplifies  through 
a  microphone  contact  which  controls  a  local  circuit.  The 
telefunken  amplifier  is  similar  but  employs  a  number  of 
such  telephone-transmitters  of  special  reed  type  in  cas- 


246 


Experimental  Wireless  Stations. 


cade  so  that  the  amplified  current  of  one  circuit  actuates 
the  next,  etc.  A  similar  device  employing  a  liquid  micro- 
phone instead  of  a  contact  device  has  been  brought  out 
by  L.  Bishop  and  a  few  are  in  use.  Microphonic  ar- 
rangements give  amplifications  of  20  upwards  but  are 
difficult  to  keep  in  adjustment  and  in  general  unreliable. 

TRANSCONTINENTAL  WIRELESS 
TELEPHONE. 

In  1915  wireless  telephone,  one  way  communication 
was  established  from  Arlington,  Va.,  to  Paris,  France; 
Honolulu,  Hawaii;  Colon,  Panama,  and  a  few  other 


FIG.  36. 


points.  No  details  of  the  circuits  used  have  been  pub- 
lished at  this  writing,  but  on  the  basis  of  the  author's 
own  independent  experiments,  previous  to  the  above 
mentioned  tests,  it  is  probable  that  the  circuits  employed 
were  of  the  type  shown  in  fig.  96.  There  are  various 
modifications  for  the  same  result.  « 


Supplement.  247 


In  this  figure  the  current  from  a  telephone  line  is 
amplified  through  an  audion  bulb  in  the  manner  already 
set  forth  and  this  amplified  current  is  used  to  actuate  the 
grid-filament  circuit  of  a  large  number  of  highly  evacu- 
ated bulbs  connected  in  parallel  and  arranged  to  gener- 
ate undamped  waves  after  the  manner  already  set  forth. 
An  ordinary  telephone  transmitter  may  thus  be  used  to 
vary  the  strength  of  the  high  frequency  oscillations  set 
up  in  several  hundred  bulbs  and  where  one  bulb  is  shown 
in  the  diagram  it  will  be  understood  that  any  suitable 
number  of  bulbs  may  be  substituted  in  a  similar  manner 
to  secure  higher  power.  Continuous  radiation  occurs  in 
the  aerial-ground  circuit  and  this  is  modified  in  exact 
accordance  with  the  voice  which  causes  the  original 
variations  of  the  electrical  current  which  are  amplified 
and  made  to  control  the  larger  current  at  radio-fre- 
quency. This  will  be  readily  understood  by  bearing  in 
mind  the  previous  discussions  of  the  parts  here  com- 
bined. Any  receiving  station  with  a  sensitive  detector 
such  as  an  audion  with  amplifying  circuit  can  receive 
from  such  a  wireless  telephone  station  and  the  voice 
reproduction  will  be  even  better  than  over  land  lines. 

LONG  WAVE  LENGTH  STATIONS. 

There  are  only  a  few  stations  of  very  long  wave 
length  now  in  operation  and  a  number  of  these  are  of 
the  undamped  wave  type.  Wave  lengths  of  6,000  to 
14,000  meters  may  be  employed,  though  12,000  meters 
is  the  most  recent  limit  for  long  distance  work.  It  is 
considered  quite  a  feat  for  an  amateur  to  hear  such  sta- 
tions. This  may  be  easily  done,  however,  either  by  con- 
structing a  long  receiving  aerial  or  by  loading  an  ordinary 
aerial  with  inductance.  A  suitable  long  wave  receiving 


248  Experimental  Wireless  Stations. 

aerial  may  consist  of  a  single  No.  14  wire  supported  about 
thirty  feet  from  the  ground  and  1,000,  3,000  or  even 
5,000  feet  long,  preferably  running  in  a  straight  line 
and  insulated  at  the  supports.  Another  method  which 
may  work  if  conditions  are  right  is  to  simply  connect 
the  aerial  terminal  of  the  receiving  set  to  one  binding 
post  of  a  small  variable  condenser,  the  other  binding  post 
of  which  is  connected  to  one  of  the  wires  of  a  telephone 
line.  When  this  is  done  no  telephone  conversation  can 
be  heard,  but  the  telephone  system  is  used  as  an  aerial 
and  brought  to  a  suitable  wave  length  by  means  of  the 
series  variable  condenser.  All  the  other  connections  and 
tuning  are  the  same  as  usual. 

LOOSE  COUPLERS  FOR  LONG  WAVE 
LENGTHS. 

Tuners  for  long  wave  lengths  simply  are  made  larger 
with  more  turns  of  wire  and  should  be  constructed  with 
taps  at  intervals  so  that  adjustments  may  be  made.  To 
say  that  a  certain  tuner  has  a  certain  wave  length  is 
misleading,  as  wave  length  depends  upon  the  product  of 
capacity  and  inductance  as  pointed  out  in  the  text  where- 
as the  tuner  itself  is  only  used  to  supply  a  portion  of  the 
inductance. 

The  accompanying  table  gives  data  which  will  serve 
as  a  guide  in  constructing  loose  couplers  of  correct 
dimensions.  These  were  calculated  by  taking  the  aver- 
age capacity  of  a  large  number  of  aerials  from  the  small- 
est to  the  largest  into  account.  The  variable  condenser  to 
be  used  in  the  secondary  circuit  should  have  a  maximum 
capacity  of  about  .0009  Mfds.  If  a  crystal  detector  is  to 
be  used  and  about  one-third  of  this  if  an  audion  detector 


Supplement.  249 


is  to  be  employed.  In  practice  only  about  three-tenths 
of  the  condenser  capacity  may  be  needed.  More  turns 
are  used  for  the  secondary  in  the  case  of  audion  detec- 
tors because  they  are  potentially  operated  devices  of 
high  resistance  and  work  best  with  large  secondary 
inductance  and  small  capacity.  In  any  case  it  is  desir- 
able to  add  to  the  wave  length  by  means  of  series  induc- 
tance rather  than  shunt  capacity  as  Dr.  Austin  has  found 
that  the  efficiency  is  decreased  by  the  parallel  condenser. 
When  considerable  inductance  is  added  in  this  manner 
the  circuit  is  said  to  be  "stiffened"  and  this  is  supposed 
to  slightly  reduce  trouble  from  static.  See  fig.  97. 

Loading  coils  for  long  wave  lengths  may  be  con- 
structed in  the  same  way  as  the  primary  coils  given  in 
the  table.  In  loading  a  small  aerial  to  a  long  wave 
length  both  the  primary  and  secondary  circuits  should 
be  loaded  as  the  ordinary  secondary  of  the  receiving 
loose  coupler  alone  is  not  large  enough.  The  loading 
coils  in  the  two  circuits  may  be  coupled  together  like 
loose  couplers  or  separated  like  straight  tuners.  The 
large  cores  may  be  made  by  wrapping  many  layers  of 
paraffined  paper  around  a  cylinder  and  removing  this 
tube  when  cold. 

Wave  lengths  less  than  the  maximum  capacity  may 
be  had  by  taking  out  taps  at  intervals  to  a  switch. 

TABLE  FOR  LOOSE  COUPLERS  AND  LOADING 
COILS. 

WAVE  LENGTH.    3,000  METERS. 

Primary:    core  4%"   long  by  4"   diameter,  tightly 

wound  with  a  single  full  layer  of  No.  26  S.  S.  C.  wire. 

Secondary:  core  3%"  diameter  by  4"  long,  wound 


250  Experimental  Wireless  Stations. 

tightly  with  a  single  layer  of  No.  28  S.  C.  C.  wire  for 
use  with  crystal  detector  or  with  No.  34  for  use  with 
audion. 

WAVE  LENGTH.    6,000  METERS. 

Primary:  core  8"  long  by  5"  diameter  wound  with 
single  layer  of  No.  24  S.  C.  C.  wire. 

Secondary:  core  7%"  long  by  4%"  diameter,  wound 
with  a  single  layer  of  No.  30  S.  C.  C.  wire  for  use  with 
crystal  detector  or  with  No.  34  wire  for  use  with  audion. 

WAVE  LENGTH.    14,000  METERS. 

Primary:  core  7%"  diameter  by  12"  long  wound 
tightly  with  single  layer  of  No.  24  S.  C.  C.  wire. 

Secondary:  core  11^2"  long  by  7"  diameter  wound 
with  single  tight  layer  of  No.  30  S.  C.  C.  wire  for  crystal 
detector  use  or  with  No.  34  wire  for  audion  circuit. 

With  small  aerials  an  additional  primary  loading  coil 
of  similar  dimensions  may  be  required  in  series  with  the 
primary  coil.  An  aerial  intended  for  only  200  meters 
has  been  successfully  loaded  to  8,000  meters  and  has 
received  signals  over  4,000  miles  with  the  aid  of  an 
amplifying  audion  detector. 

DEAD  ENDS. 

The  unused  portion  of  a  tuning  coil  or  cover  is  said  to 
be  "dead"  and  may  absorb  some  energy  thus  reducing  the 
efficiency.  This  is  almost  eliminated  by  switching  ar- 
rangements which  entirely  cut  out  the  unused  turns. 
The  principle  is  shown  in  figure  98  which  shows  dia- 
grammatically  a  form  of  switch  constructed  by  the 
author  for  this  purpose.  Only  the  primary  is  here  shown 


Supplement. 


251 


as  the  secondary  winding  may  be  arranged  in  the  same 
way. 

A  wide  range  of  wave  lengths  is  thus  possible  in  a 
single  receiving  set.  The  coil  is  divided  into  a  number 
of  insulated  series  of  turns  O,  O,  etc.,  which  are  con- 
nected to  a  switch  built  like  a  commutator  so  that  con- 


PfMMAf\Y 


r 
I 


SECONDARY 


FIG.  $7 


no.  38 


tacts  P,  P,  P,  etc.,  may  successively  cause  additional 
turns  to  be  included  in  the  circuit  while  at  the  same  time 
unused  turns  at  the  other  end  of  the  coil  are  open  cir- 
cuited so  that  they  cannot  absorb  the  energy.  Contact 
with  the  ground  is  made  through  slip  ring  Q  which 
rotates  with  the  switch.  Each  contact  P,  P,  is  of  course 
insulated  from  the  others  and  all  are  placed  at  equal 
intervals. 


252  Experimental  Wireless  Stations. 

PLURAL  RECEIVING  SETS. 

Another  plan  is  to  make  a  number  of  separate  and 
independent  receiving  sets  or  couplers,  each  exactly  right 
to  receive  at  a  certain  wave  length  or  from  a  certain 
station.  A  switch  is  then  made  to  put  the  desired  set 
in  and  the  others  are  not  in  use  at  such  time. 

TRANSMISSION  OF  TIME  SIGNALS  BY  NAVAL 
RADIO  STATIONS. 

To  receive  time  signals  an  aerial  about  500  feet  long 
is  desirable  though  a  much  smaller  one  will  do.  Appar- 
atus described  in  this  book  will  bring  in  the  signals  with 
either  a  crystal  or  audion  type  of  detector.  The  follow- 
ing new  advice  is  given  by  the  U.  S.  Dept.  of  Commerce : 

Time  signals  are  now  sent  out  on  the  Atlantic  coast 
only  through  the  radio  stations  at  Arlington,  Key  West, 
and  New  Orleans.  Signals  from  Arlington  and  Key 
West,  which  reach  a  zone  formerly  served  by  other  coast 
stations,  are  sent  out  every  day  in  the  year  twice  a  day, 
viz,  from  n  -.55  a.  m.  to  noon  and  from  9.55  to  10  p.  m., 
seventy-fifth  meridian  time.  Time  signals  from  New 
Orleans  are  sent  out  daily,  including  Sundays  and  holi- 
days, commencing  at  11.55  a-  m->  seventy-fifth  meridian 
time,  and  ending  at  noon. 

On  the  Pacific  coast  the  time  signals  are  sent  broad- 
cast to  sea  through  the  naval  radio  stations  at  Mare  Is- 
land, Eureka,  Point  Arguello,  and  San  Diego,  Cal.,  and 
at  North  Head,  Wash.  The  controlling  clock  for  each 
station  is  in  the  naval  observatory  at  the  Mare  Island 
Navy  Yard.  Signals  from  Mare  Island  are  sent  out 
every  day  from  11.55  to  noon,  and  from  9.55  to  10  p.  m., 
one  hundred  and  twentieth  meridian  standard  time. 


Supplement.  253 


Those  from  North  Head,  Eureka,  Point  Arguello,  and 
San  Diego  are  sent  out  daily,  excluding  Sundays  and 
holidays,  from  11.55  to  noon,  one  hundred  and  twentieth 
meridian  standard  time. 

To  get  the  maximum  clearness  of  signals,  the  receiv- 
ing circuit  should  be  tuned  to  that  of  the  sending  station. 
Arlington  and  Mare  Island  send  on  a  2,5OO-meter  wave 
length,  North  Head  and  San  Diego  on  a  2,ooo-meter 
wave  length,  Eureka  on  a  i,4OO-meter  wave  length, 
Key  West  and  New  Orleans  on  a  i,ooo-meter  wave 
length,  and  Point  Arguello  on  a  75O-meter  wave  length. 

TRANSMISSION   OF  WEATHER  REPORTS   BY 
NAVAL  RADIO  STATIONS. 

Through  co-operation  with  local  offices  of  the  United 
States  Weather  Bureau,  weather  forecasts  are  sent  broad- 
cast to  sea  through  naval  coast  radio  stations  at  certain 
times,  varying  with  the  locality.  Storm  warnings  are 
sent  whenever  received  and  the  daily  weather  bulletins 
are  distributed  by  the  naval  radio  stations  at  Arlington, 
Va.,  and  Key  West,  Fla.,  a  few  minutes  after  the  10 
p.  m.  time  signal.  These  bulletins  consist  of  two  parts. 

The  first  part  contains  code  letters  and  figures  which 
express  the  actual  weather  conditions  at  8  p.  m.,  seventy- 
fifth  meridian  time,  on  the  day  of  distribution,  at  certain 
points  along  the  eastern  coast  of  North  America,  one 
point  along  the  Gulf  of  Mexico,  and  one  at  Bermuda. 

The  second  part  of  the  bulletin  contains  a  special 
forecast  of  the  probable  winds  to  be  experienced  a  hun- 
dred miles  or  so  off  shore,  made  by  the  United  States 
Weather  Bureau,  for  distribution  to  shipmasters.  The 
second  part  of  the  bulletin  also  contains  warnings  of 


254  Experimental  Wireless  Stations. 

severe  storms  along  the  coasts,  as  occasions  for  such 
warnings  may  arise. 

Immediately  following  this  bulletin,  a  weather  bul- 
letin for  certain  points  along  the  Great  Lakes  is  sent 
broadcast  by  the  naval  radio  station  at  Arlington,  Va., 
consisting  of  two  parts.  The  first  part  contains  code  let- 
ters and  figures  which  express  the  actual  weather  condi- 
tions at  8  p.  m.,  seventy-fifth  meridian  time,  on  the  day 
of  distribution,  at  certain  points  along  the  lakes.  The 
second  part  of  the  bulletin  contains  a  special  forecast 
of  the  probable  winds  to  be  experienced  on  the  lakes, 
during  the  season  of  navigation — about  April  15  to 
December  10. 

The  points  for  which  weather  reports  are  furnished 
are  designated  as  follows :  For  Atlantic  coast  and  Gulf 
points,  S= Sydney,  T=Nantucket,  DB=Delaware 
Breakwater,  H=Hatteras,  C= Charleston,  K— Key 
West,  P=Pensacola,  and  B= Bermuda;  for  points  on 
the  Great  Lakes,  Du=Duluth,  M=Marquette,  U= 
Sault  Ste.  Marie,  G=Green  Bay,  Ch=Chicago,  L= 
Alpena,  D^Detroit,  V=Cleveland,  and  F=Buffalo. 

All  bulletins  begin  with  the  letters  U.  S.  W.  B. 
(United  States  Weather  Bureau)  and  the  weather  con- 
ditions follow.  The  first  three  figures  of  a  report  rep- 
resent the  barometric  pressure  in  inches  (002=30.02)  ; 
the  next  figure,  the  fourth  in  sequence,  represents  the 
direction  of  the  wind  to  the  eight  points  of  the  compass : 
i=north,  2=northeast,  3=east,  4= southeast,  5=south, 
6=southwest,  7^=west,  8=northwest,  and  o=calm.  The 
fifth  figure  represents  the  force  of  the  wind  on  the 
Beaufort  Scale,  given  on  page  255. 


Supplement. 


255 


Beaufort  Scale  of  Wind  Force. 


Number    and    designation. 

Statute  miles 
per  hour. 

Nautical 
miles  per 
hour. 

0  Calm 

0  to  3 

0  to  2  .  6 

8 

6.9 

2  Light    breeze            •        

13 

11.3 

3  Gentle    breeze                

18 

15.6 

23 

20.0 

28 

24.3 

34 

29.5 

7  Moderate  gale              

40 

34.7 

8  Fresh   gale 

48 

41.6 

56 

48.6 

10  Whole  gale              

65 

56.4 

1  1  Storm               

75 

65.1 

f             90 

78.1 

In  order  to  simplify  the  code,  no  provision  has  been 
made  for  wind  force  greater  than  9,  strong  gale,  on  the 
Beaufort  Scale.  Whenever  winds  of  force  greater  than  9 
occur,  the  number  representing  them  is  given  in  words 
instead  of  figures,  thus  :  Ten,  eleven,  etc. 


Example  of  Code. 


e  . 

U  S  W  B    Du  95826    M  97635    U  00443    G 
Ch  95667    L  00644    D  00842    V  01054    F  01656 


96046 


Translation. 

United    States    Weather    Bureau. 


Station. 

Pressure. 

Wind. 

Direction.   |      Force.l 

Duluth                 

29.58 
29.76 
30.04 
29.60 
29.56 
30.06 
30.08 
30.10 
30.16 

1 

NE 
E 
SE 
SE 
SW 
SE 
SE 
S 

1 

6 

5 
3 
6 
7 
2 
4 
4 
6 

Marquette                

Sault  Ste    Marie          

Green  Bay      

Alpena   .            

Detroit                

Cleveland  

Buffalo   

i  See    Beaufort    scale. 


256 


Experimental  Wireless  Stations. 


U.  S.  PATENTS  ON  WIRELESS  TELEGRAPHY, 
TELEPHONY,  AND  CONTROL. 

This  is  the  most  complete  list  obtainable.  It  should 
be  invaluable  to  the  reader.  Patents  from  1881  to 
January  i,  1916,  are  included. 

HOW  TO  USE  THE  LIST. 

Look  for  the  subject  of  interest  or  the  headings  that 
might  contain  it.  Patents  considered  of  particular  im- 
portance have  been  designated  with  a  *  mark.  Copies 
complete  of  any  of  these  patents  can  be  obtained  for 
5  cents  each  by  addressing  the  Commissioner  of  Patents, 
Washington,  D.  C. 


GENERAL    APPARATUS    AND    SYSTEMS,    BOTH    TRANSMIT- 
TING AND  SENDING. 

For  any   other   apparatus   or  arrangement   of   circuits   consult   also   this 
S:neral    list,    as    it    includes    patents    treating    of    more    than    one    related 
ea. 

Patents 

numbered  : 

586,193 

716,334 

1,123,118* 

1,120,054 

711,266 

711,184 

717,773 

717,769 

717,771 

717,772 

711,183 

711,182 

749,584 

748,597* 

734,048 

730,247* 

743,999 

749,370 

749,131 

737,170* 

800,854 

12,073 

758,842 

706,718 

756,904 

730,819* 

756,719* 

802,981 

805,412 

716,334 

765,298 

706,742* 

710,355 

710,354 

703,842 

768,301* 

710,122 

706,746* 

706,745 

706,743 

706,500 

763,893 

706,741* 

671,406 

711,132* 

11,952 

700,250* 

671,407 

680,001 

757,559* 

687,440 

737,072 

699,158 

795,762 

682,974 

684,706 

706,736* 

684,467 

758,005* 

750,496 

753,863* 

720,568* 

708,071 

609,154* 

711,130 

708,072 

12,168 

703,712 

706,737* 

706,740 

707,064 

717,766 

743,056* 

750,429* 

671,732 

696,715 

685,742 

741,622 

763,772* 

716,203 

717,765 

768,003* 

674,846* 

664,869 

377,879 

691,176 

550,510 

657,224 

651,361 

651,362 

650,255 

651,014 

650,110* 

650,109 

647,009* 

657,222 

711,174* 

644,497 

627,650* 

647,007* 

647,008* 

643,018 

673,553 

673,418 

716,203 

671,403 

929,745 

783,923* 

781,823 

716,000 

962,014* 

934,883" 

935,721 

842,910 

837,616 

837,901* 

841,386 

889,790 

889,792 

884,109* 

889,791 

884,070 

884,076 

957,282* 

884,108 

884,106* 

962,017 

884,071 

899,239 

899,243 

1,129,821 

728,243 

701,256 

884,986* 

729,797 

768,778 

1,006,786 

1,128,210 

730,246 

897,278* 

879,409 

913,718 

998,567* 

908,815* 

994,191 

706,738 

717,770 

894,378 

754,058 

727,329 

727,330 

730,753 

767,979* 

767,983 

927,641 

770,668* 

752,895 

874,745 

768,000 

884,987* 

802,430 

783,992* 

786,132* 

770,229 

759,216 

767,984 

759,825 

711,444 

760,463* 

725.635 

749,434 

749,178 

742,779 

1,162,830 

12,169 

Supplement. 


257 


Patents  numbered 


General   Systems,   Continued. 


706,737 

767,990* 

767,985* 

767,991* 

725,634* 

767,989* 

767,988* 

734,476 

753,864 

808,641* 

768,003 

818,236 

771,818 

767,978 

923,963 

764,093 

974,762* 

966,705* 

764,094 

1,111,777 

929,145 

926,936 

879,532 

997,515 

1,059,666* 

1,106,875 

1,038,506 

1,106,874 

899,240 

986,651 

935,382* 

916,307 

827,524 

884,107 

858,569 

1,020,032* 

1,132,568* 

1,019,236* 

1,080,271* 

1,018,555 

813,914* 

954,640* 

979,276 

808,594* 

802,432* 

1,074,423* 

996,090 

996,088 

1,001,227 

706,740 

1,157,094 

767,987* 

767,980* 

767,986 

767,981 

767,975 

725,636 

767,977* 

767,982* 

767,976* 

758,517 

781,873 

813,975 

802,417 

768,005 

768,002 

767,996* 

929,349 

1,018,555 

759,826 

768,004 

884,989* 

864,272 

884,110 

935,383 

956,165 

706,735* 

793,650 

913,528 

793,652 

1,014,002* 

946,168 

934,875 

929,487 

1,031,698 

1,101,915* 

824,003 

899,242 

889,289 

822,936 

937,281 

1,010,669 

924,560* 

928,962 

1,016,003 

1,101,533* 

1,015,881 

1,003,375 

1,006,635 

1,006,636 

1,012,456 

758,527 

761,450 

802,418 

739,287* 

1,020,032 

797,544* 

730,753* 

742,780 

1,002,049 

958,006 

749,372 

824,676 

767,995 

768,001 

767,997 

767,992 

767,998 

767,993 

829,787 

908,742 

901,649 

992,042 

711,131 

785,803 

711,445 

962,018 

624,516* 

797,169* 

1,128,210 

1,045,781 

1,132,569* 

1,114,840 

1,138,652 

928,371* 

956,489 

946,166 

851,621 

854,813 

869,714 

899,241 

714,648 

1,050,728 

1,074,456 

1,059,665 

1,082,221 

1,035,334* 

716,334 

730,819 

1,123,119 

1,139,226 

14,012 

806,966 

756,720 

788,477 

843,733 

776,337 

782,181 

787,780 

755,846 

771,819 

792,528* 

767,999* 

767,994 

943,969 

935,386 

946,167 

965,060 

1,002,051* 
1,101,914* 

915,280 
1,014,002* 

996,580 
802,431 

995,339 
802,421 

929,145 
802,420* 

711,181 
802,419* 

1,127,921* 
444,678* 

818,363 

840,909 

992,791 

676,332* 

680,002 

716,000 

713,700 

758,004 

714,246 

960,304 

850,917 

1,021,132 

1,045,782 

1,080,544 

1,050,441 

1,022,540* 

750,216 

918,306 

918,307 

777,014 

1,158,123 

RECEIVING   DEVICES,    SYSTEMS,    AND    CIRCUITS. 

Includes    selective    arrangements,    interference    compensators,    beat    re- 
ceivers, audio-tuning,  bridge  circuits,  apparatus  arrangements,  static  shields, 
etc.      See   also    related   headings.      Includes    some    detectors. 
Patents    numbered : 

1,116,183     1,116,588 
1,132,588*   1,139,632 


1,895,342  1,138,147  1,144,968 

1,113,149*  997,516*  1,134,593 

1,127,368  727,327  762,829  767,971 

761,258  712,764  806,052  962,417 

921,531*  727,331*  995,312  936,258 

780,842  902,613  897,779  962,015 

883,437  936,258  962,015*  958,181* 

902,613  936,163  912,726  974,985 

761,258  727,331  884,988  748,306 

727,328*  746,557*  745,463  737,271 

773,171  773,340  774,922  775,050 

783,712  961,645*  1,002,150  758,468 

888,191  959,510  892,312  896,130 

1,009,317  963,173  916,429*  918,618 

784,762  931,586*  925,921  802,428* 

852,381*  853,929  839,029*  706,745 

923,699*  857,375  994,426  858,668 

812,557  820,169  816,205  962,417 

1,089,091  13,798  1,042,778  1,097,974 

1,059,391*  1,022,539  1,044,637*  1,087,892 

897,278  752,894  752,895  1,018,155 

1,156,677  1,163,839 

SELECTIVE  SECRECY  SYSTEMS. 

(See  also  others.) 
Patents   numbered : 

1,102,442  1,091,768  714,384  715,203        717,978        714,756 

752,894  727,326  12,149  714,831           12,141      1,123,119* 

913,718  768,001*  1,091,768 


801,118 

668,315" 
12,115 

962,016 

974,986 

892,312 

796,403 

744,936 

782,422 

905,537 

877,451* 

974,927 

824,682* 

730,247 

846,081* 
1,093,240 
1,027,238 

1,087,549*   1,132,568 
1,012,496        716,135 


1,019,236*  657,223 
1,143,799  1,123,910 
767,922 
793,648* 
665,957 
836,531 
921,531* 
730,246 
749,371* 
755,586 
780,842 
924,827 
886,154 
952,403 
846,414 
802,422* 


796,800 

974,838 

962,016 

845,316 

974,538 

706,742 
12,115 

756,219 

793,648 

897,779* 

883,241 
1,012,496 

930,508 

802,423* 

785,276       .       . 
1,087,113*   1,104,256 
1,091,127     1,099,865 


1,009,106 


916,429 
167,970 


795,840 
777,014 


258 


Experimental  Wireless  Stations. 


DETECTORS. 

Oscillation    Responding    Devices,    Rectifiers,    Electrolytic,    Heat,    Contact, 

Capillary   Devices,   etc. 
(For  circuit  arrangements,  etc.,  see  Receiving  Apparatus  and  Systems.) 


Patents  numbered : 


Patents   numbered 
772,878        877,069 
715,043 


OSCILLAPHONE. 

769,005        819,779 

MAGNETIC   DETECTOR. 

917,104   930,780    711,182 


917,104    749,371 


ELECTRO-CAPILLARY   DEVICES. 
Patents   numbered: 
844,080        798,484        798,483        798,482        798,481        848,083 


902,569 
727,331 


ELECTROLYTIC. 

Patents   numbered  : 

706,742  716,334  929,784  894,317*  875,105 
894,317  875,105  962,014*  783,712  716,203 
731,029  706,744  916,428  793,648  768,003 

HEAT   DETECTOR. 
Patents  numbered:    800,856        767,996        767,997 


BOLOMETER. 

Patents   numbered  : 
778,275        767,992        767,980        767,971        767,981        767,972 

CRYSTAL   AND    MISCELLANEOUS—  ALL    TYPES. 


795,312 
716,000 


Patents   numbered  : 

879,062 

879,117 

923,700 

924,827 

837,616 

886,154 

912,613 

912,726 

1,159,969 

1,152,444 

1,158,112 

1,162,765 

1,080,681 

1,052,355 

1,096,142* 

1,048,117 

1,102,184 

1,104,065 

1,104,073* 

867,876* 

899,264 

824,637* 

824,638* 

927,314 

1,013,223 

986,806 

966,855 

954,619 

959,967 

867,878 

867,877 

912,613 

879,062 

917,574 

1,004,784 

904,222 

906,991 

811,654 

776,359 

757,802 

741,570 

1,003,210 

905,781 

901,942 

962,262 

836,070* 

836,071* 

1,155,338 

879,061 

820,258 

902,569 

706,744 

707,266 

711,123 

756,676 

787,412 

1,003,374 

902,569 

1,136,044 

1,136,045 

1,137,714 

1,136,046 

1,136,047 

1,122,558 

1,128,552 

1,118,228 

1,115,902 

1,112,411 

1,145,658 

1,144,399* 

1,008,977* 

933,263 

770,228 

917,574 

706,735 

706,736 

767,985 

837,616 

706,735 

MERCURY  AUDION,  VACUUM  VALVES,  AUDIONS,  THERMI- 
ONIC  RELAYS,  AND   DETECTORS. 


Patents 
1,130,008 
837,901 
1,127,371* 
1,145,735 
943,969 
837,901 

numbered 
1,142,625 
867,876 
1,430,008 
1,144,596 
824,637 
841,387 

837,878 
995,126 
1,128,817 
1,159,307 
824,638 
867,877 

836,070 
836,071 
1,130,009 
1,138,652 
867,071 
867,878 

879,532 
979,275* 
1,130,042* 
1,113,149 
915,280 

841,386 
803,689* 
1,128,280 
841,397 
824,637 

979,275 
1,130,043 
1,137,275 
1,156,625 
803,684 

Supplement.  259 


COHERORS. 

(See  Radio-Mechanical   Control.) 
Patents   numbered : 

1,019,260        932,799*      700,708        691,815        993,024        886,983        794,459* 
800,119*      908,504        985,854        775,113         742,298         763,894         759,835 
968,007        670,711        708,070        755,840        722,139*      710,372     1,019,260 
741,767     1,118,410    1,150,111 

WAVE  'METERS. 

Patents   numbered: 

804,189,  1,064,325  1,018,769  804,190  932,819  846,675  918,256 
892,311  993,316  1,152,632 

GALVANOSCOPE. 

Patent   numbered   798,152 

SYNCHRONIZER. 

Patent    numbered    717,768 

RANGE    FINDER. 
(See   also   Direction    Finders.) 
Patents  numbered:    749,436*  1,135,604* 

SPARK    GAPS,    INCLUDING   MUFFLED,    COOLING   AND   TONE 
TYPES. 

Patents   numbered : 

1,073,371  1,051,744  1,075,075*  834,054  926,933  971,935*  1,132,589* 
1,117,681  750,180  750,005  1,163,586  792,014  706,741  768,000* 
1,148,521*  1,161,520  1,152,272  1,162,659 

WIRELESS   TELEPHONY. 

(See  also  Oscillation  Producers,  Transmitting  and  Sending  Systems,  etc.) 

Patents   numbered : 

1,118,004  1,125,496*  1,122,594  1,139,413  1,062,179*  1,086,530  1,108,895* 

1,044,798  1,052,£49  1,088,686    803,199*   836,015*   814,942    836,072* 

803,513*  1,006,429    923,962    753,863    793,649    793,750  1,148,827 

RADIO-MECHANICAL  CONTROL.     TORPEDOES,  TYPEWRITERS, 
ETC.,    CONTROLLED    BY    WIRELESS.      COHERORS. 

(See  also  Detectors  and  Systems.) 

715,803  1,115,530*  1,097,871  1,072,152  1,987,966  625,823  1029,573 
789,618  976,500  828,864  907,488  1,098,379*  957,001  663,400 
723,176  913,814  1,155,653  1,154,628  1,149,874 

RECEIVING   RECORDER. 

Patent   numbered   766,743 

RELAYS  AND  RELAY  SYSTEMS. 

Patents    numbered : 

717,514*      786,696*      657,221*      718,535        717,513        717,509        717,570 
J,106,729        655,716 

AUTOMATIC  TICKER. 
(See    also    Receiving    Devices.) 
Patents  numbered:     1,098,380     1,161,142 


260  Experimental  Wireless  Stations. 


TUNING    DEVICES    AND    COUPLINGS. 

(See    also    Receiving    Systems,    Transmitting    Systems,    Wavemeters.) 
Patents   numbered : 

1,116,130        978,604        802,425      1,070,376     1,014,722     1,014,722*    1,083,085 
1,096,065        719,005        707,056        763,345*      717,511*      934,296        803,569 
956,936     996,092         717,512*    1,132,568      1,127,921         714,756         714,831 
1,151,098     1,148,279 

AMPLIFIERS   FOR   RECEIVING. 

(See    also    Receiving    Systems,    and    Audions.) 
Patents   numbered: 

965,884        714,832     1,041,210          12,151  12,152     1,163,180        751,818 

714,833     1,165,454 

ALARM   SYSTEM. 

(See    Coherers,    and    Radio-Mechanical    Control.) 
Patent  numbered  606,405 

CONDUCTION  AND  EARTH  SYSTEMS. 

(See    general    system   list.) 
Patents  numbered:     1,051,443*      690,151 

COMBINATION    SETS.      RECEIVING    AND    TRANSMITTING. 

LINE  AND   RADIO. 
Patents  numbered:    996,089     1,104,712     1,092,294        916,483        972,721 

PORTABLE  STATIONS. 

(See   general  list  and  Aerials.) 
Patents  numbered:     1,145,066        958,209 

COMBINATION    TRANSMITTING    AND    RECEIVING    SETS. 

(See  also  general   list.) 
Patents   numbered : 

1,116,111  1,141,453  1,141,386  751,294  777,014  736,483  726,413 
840,908  979,144  916,895  876,281  794,334  798,158  810,150 
793,652 

TRANSFORMERS     RESONANT    WITH     CAPACITY,    FOR    TRANS- 
MITTING   STATIONS. 

Patents  numbered:    965,168*      835,023* 

DIRECTION  AND  DISTANCE  FINDERS. 

Patents  numbered : 

736,432  744,897        716,135  1,069,355  899,272           12,148        941,565 

943,960*  961,265         984,108  948,086*  945,440*      894,318      1,002,141 

833,034  716,134        758,517  1,149,123  1,149,122 

STATIONARY    AND    PORTABLE    ANTENNA— AEROPLANE, 
AERIALS. 

Patents   numbered: 

1,141,387        918,255        919,115        930,746  898,197  945,475  972,004 

959,100     1,005,471*      793,718        793,651  948,068  860,051  1,106,945 

1,101,175     1,063,671      1,132,569        767,973  717,511  706,737  1,147,010 

770,229        749,436        749,131        748,597  771,819  707,746  706,738 


Supplement.  261 


Aerials,  Continued. 

706,739  716,136  899,272  1,158,124  717,512  793,718  753,864 
802,981  802,982  806,966  822,936  824,003  767,986  767,988 
767,998  767,999  716,177  1,165,412 

BREAKING    SYSTEMS    AND    KEYS—SENDING    TO     RECEIVING. 

Patents  numbered:    827,523        842,134     1,016,564*   1,073,624 

MASTS— AERIAL  SUPPORTS,  INCLUDING  AEROPLANE  AERIAL 
DEVICES. 

Patents  numbered:  1,116,059        857,152     1,034,760     1,099,861        768,005 

AUTOMATIC    CHANGE-OVER   SWITCH— SENDING   TO    RE- 
CEIVING. 

Patent  numbered  1,074,057 

CLEARING  ICE  FROM  ANTENNAS. 

Patent  numbered    750,181 

PROTECTING   DEVICES. 

Patents  numbered:    771,820        978,607     1,035,958 

CONDUCTOR   FOR    WIRELESS    TELEGRAPHY. 

Patent   numbered    706,739 

CURRENT  INTERRUPTER. 

(General    interrupters    not   included.) 
Patent  numbered  1,039,011 

KEYS,    CIRCUIT   CLOSERS    AND    CONTROLLERS. 

Patents   numbered: 
917,749        792,020*      792,015        769,228        934,716        749,178        792,015 

TRANSMISSION   OF   MUSIC. 

(See    Radiotelephony.) 
Patent   numbered    1,025,908 

PUNCHED  TAPE  SYSTEMS. 

Patents   numbered : 
725,634        725,635        725,636        767,978        767,991        767,932        767,995 

STATIC   VALVE.      STATIC    PREVENTION. 

Patents  numbered:    823,402        825,402 

METHOD   OF   UTILIZING  ENERGY  OF  WAVES. 

(See    general   list.) 
Patent    numbered    731,029 

VISIBLE   AND    AUDIBLE    SIGNAL. 

(See  Coherors,   Radio-Mechanical   Control,   etc.) 
Patent  numbered  805,714 


262  Experimental  Wireless  Stations. 

COMMUNICATION     BY    WAVE    COMPONENTS. 

(See   also    General   Systems.) 
Patent    numbered    876,996 

PRODUCTION    OF    TONE    EFFECTS. 
(See  also  Spark  Gaps,   General   Systems,   Transmitters.) 
Patents   numbered:     1,056,892*    1,056,893* 

AUTOMATIC    COMMUTATOR    FOR   WIRELESS    TELEGRAPHY. 

(See   General  Systems   also   for   similar  arrangements.) 
Patent   numbered    1,105,029 

RELAYING  HIGH  FREQUENCY  CURRENTS. 

(See  also  Audions,   Detectors,   Oscillation   Producers,   etc.) 
Patent    numbered    1,042,069* 

DETERMINATION  OF  FREQUENCY. 

(See   also   Wavemeters.) 
Patent    numbered    1,022,584 

SYSTEMS    OF    HIGH    FREQUENCY    DISTRIBUTION. 

(See   also    General    Systems,    Transmitters,    Oscillation    Producers.) 
Patents    numbered : 
1,123,098*   1,122,027*      856,149*      856,150*   1,043,104*   1,043,766* 

CONTROL    OF    SPARK    PRODUCTION. 

(See   also    Radiotelephony   and   General    Systems.) 
Patents   numbered:     750,180        802,850 

TELEPHONE    RECEIVER. 

(General   telephone    list   not   included.) 
Patent   numbered   936,684 

DUPLEX,   MULTIPLEX,   SYSTEMS. 

(See   General    Systems.) 
Patents   numbered : 

716,136        772,829        802,429        802,426        717,767        767,970        924,168* 
1,116,309*   1,076,312     1,042,205        749,434        720,568        716,134        772,879 
767,980        716,134        793,652 

SUBMARINE   SIGNALLING   SYSTEMS,    COLLISION   PRE- 
VENTION,  ETC. 
Patents   numbered: 

711,386     1,126,095     1,073,088        749,694        802,020        914,483        913,910 
526,609     1,099,998 

PHOTOPHONES. 

(See    General    Systems.) 
Patents    numbered : 

235,120        680,614        796,254        766,355        241,909*      235,496*      235,199 
341,213 


Supplement. 


263 


CONDENSERS,    PAPER,    GLASS,   AIR,    COMPOSITION,    ETC. 

(For  complete  list  see  general  electrical  classification  omitted  here.) 
Patents    numbered: 

1,127,513        793,647*      786,578        793,777     1,033,095     1,150,895     1,108,793 
1,063,105     1,094,178     1,116,013     1,111,289*   1,112,397     1,114,626     1,139,976 
814,951        793,647        793,651        767,977     1,151,824 

DIRECTIVE  SYSTEMS. 

Patents    numbered : 
795,762        749,131        720,568        716,134        716,135        771,818        771,819 

TRANSMISSION    SYSTEMS   AND    APPARATUS. 


(General   list.      See 


also   detail   lists,   as   they   are 
See    General    Systems.) 


not   repeated  here. 


Patents  numbered  : 

1,145,239—  Polyphase 

974,169 

1,119,952 

247,127 

255,305 

11,913 

586,193* 

657,363 

465,971 

932,821 

926,900 

767,974* 

767,973* 

749,435 

685,953 

685,954 

685,957 

785,956 

754,737 

767,977 

755,132 

775,416 

776,876 

876,165 

792,014 

787,056 

910,430 

935,381 

950,258 

932,820 

921,293 

1,005,338 

986,405* 

918,208 

1,119,732 

749,372 

802,850 

768,004 

758,004 

1,148,279 

966,539 

953,635 

927,433 

802,427* 

851,336* 

991,837 

834,497 

966,475 

917,103 

858,554 

1,015,881* 

921,013 

1,136,411* 

1,139,226 

1,140,150* 

1,141,717 
714,837 

1,126,966* 
767,990 

723,188 
767,975 

685,958 
767,976, 

685,955 
767,984 

714,832 
767,989 

714,833 
767,975 

767,979 

1,153,717* 

OSCILLATION    PRODUCERS,    ARC    CONTROLS,    PRODUCTION 

OF  HIGH  FREQUENCY  CURRENTS  AND  ALL  KNOWN 

TYPES   OF  WAVES. 

(See    Audions    and    General    systems.      This    list    includes    mercury    vapor 
devices  applied  to  the  art,  except  such  as  are  listed  elsewhere.) 

Patents    numbered : 

1,121,360  1,120,306  829,447  829,934 

500,630  1,122,975  ,131,190  ,123,120 

1,043,117  1,101,148  ,159,209  ,142,496 

1,047,643  1,103,822  ,101,491  ,061,717 

773,069  1,096,717  ,105,984  ,092,398 

932,111  966,560  ,077,733  ,028,204 

758,004  706,742  897,279  767,983 


550,630 
1,097,872 
1,139,673 
717,774 
921,526 
1,110,253 
1,109,909 
767,993 

1,115,823 
1,087,126 
790,250 
685,012 
979,277 
781,606 
^923,963 

1,118,174 
1,152,675 
1,023,135 
925,060 
780,997 
817,137 
730,755 

RELAY   OF   MESSAGE. 

Patents  numbered:    717,509        717,513        717,514 


717,516 


NOTES   ON   LIST. 

As  a  guide  to  date  of  issue,  the  number  of  the  first  patent  for  a  period 
is    given    herewith : 

247,127-1881       691,176-1902       730,247-1903       749,131-1904       802,417-1905 
808,641-1906       840,909-1907       876,165-1908       908,742-1909       945,440-1910 
984,108-1911     1,014,002-1912    1,050,728-1913    1,083,677-1914     1,123,910-1915 
Numbers  of  five  figures,  as   12,073,  are  for  re-issued  patents. 
The   author   assumes   no   liability   for   the   accuracy   of   the   list,   but   it 
is  thought  to  include  all   of  the   U.   S.   patents   granted  in  the  art.     The 
general    list    of    electrical    patents    which    overlaps    the    radio    list    in    many 
instances   has   not   been   included   because  it   alone   is   far  larger   than   the 
entire  wireless  list. 


264  Experimental  Wireless  Stations. 

DISCUSSION  OF  U.  S.  PATENTS  FOR  1914 

AND  1915. 

By  way  of  pointing  out  indications  of  recent  prog- 
ress a  few  recent  patents  may  be  mentioned.  Patents 
numbered  1,087,113  and  1,104,256  describe  the  tone 
wheel  ticker,  receiving  system  of  Rudolf  Goldschmidt. 
Patents  numbered  1,098,379,  1,154,628  and  1,115,530 
describe  the  control  system  of  J.  H.  Hammond,  Jr. 
An  improved  audion  circuit  is  given  in  patent 
1,113,149  of  E.  H.  Armstrong.  An  arc  oscillator 
using  an  arc  between  cooled  electrodes  immersed  in 
alcohol  and  said  to  have  transmitted  telephone  com- 
munication 600  miles  is  set  forth  in  Dwyer's  patent 
No.  1,109,909.  A  multiphase  transmitter  is  described 
in  patent  1,114,840.  A  practical  arrangement  of  an 
aerial  on  an  aeroplane  is  given  in  patent  numbered 
1,116,059.  The  duplex  system  of  Marconi  using  two 
aerials  at  right  angles  is  explained  in  patent  numbered 
1,116,309.  A  receiving  set  which  is  selective  and  ob- 
viates the  use  of  the  loose  coupler  by  a  practical  ar- 
rangement of  inductance  and  capacity  is  described  in 
Cohen's  patent  No.  1,123,098.  A  proposed  secrecy 
system  is  describe  by  De  Forest  in  patent  numbered 
1,123,119. 

A  suitable  system  for  radiotelephony  over  about 
fifteen  miles  is  described  by  De  Forest  in  patent 
1,125,496.  His  arrangement  uses  a  quenched  spark 
gap  oscillator.  A  balanced  receiving  circuit  which 
attempts  to  prevent  interference  is  described  in 
patent  1,127,368.  A  good  tuning  circuit  for  receiving 
with  both  tight  and  loose  coupling  is  described  in 
Tronchon's  patent  1,129,821.  Weintraub  furnishes 
much  information  on  mercury  vapor  tubes  as  oscilla- 


Supplement.  265 


tion  producers  in  patent  numbered  1,131,190.  Tape 
sending  and  phonographic  recording  is  illustrated  in 
Fessenden's  patent  1,132,568.  Marconi  describes  a 
plural  circuit  rotary  gap  method  of  generating  con- 
tinuous waves  in  patent  1,136,477.  R.  C.  Galletti 
shows  a  system  utilizing  high  frequency  unidirectional 
impulses  in  patent  1,140,150.  A  novel  aerial  loaded 
with  inductance  and  capacity  to  give  a  large  wave- 
length range  in  a  small  space  is  illustrated  by  Frank- 
lin in  patent  1,141,387.  A  good  exposition  of  the 
heterodyne  system  is  given  in  patent  1,141,717.  Pat- 
ent 1,144,969  shows  a  method  of  using  a  crystal  de- 
tector to  receive  from  undamped  wave  stations. 
P.  C.  Hewitt  describes  his  mercury  vapor  receiving 
system  in  detail  in  patent  1,144,596.  Marconi  ex- 
plains his  disc  discharger  in  patent  1,148,521.  An  im- 
proved coheror  is  illustrated  in  patent  1,150,111  and 
a  new  manner  of  using  it  for  radio  control  is  shown 
in  patent  1,155,653.  Seibt  describes  a  practical 
quenched  spark  transmitter  in  patent  1,153,717. 
Vreeland  illustrates  his  mercury  arc  generator  cooled 
by  water  in  patent  1,152,675.  An  antimony  and  ferro- 
silicon  detector  is  shown  in  patent  1,158,112.  A 
secrecy  method  is  shown  in  patent  14,012  of  Nov.  16, 
1915.  The  receiving  ticker  used  by  the  Federal 
Telegraph  Co.  is  shown  in  patent  1,161,142.  Quenched 
spark  gap  construction  is  the  subject  of  Pfund's  pat- 
ent 1,161,520.  In  patent  1,152,272  H.  Boas  makes 
the  practical  suggestion  of  using  tungsten  for  spark 
gaps.  One  form  of  the  plural  receiving  tuner  men- 
tioned on  page  252  is  described  in  patent  1,151,098. 
A  practical  quenched  spark  system  is  described  in 
patent  1,162,830.  Amplification  by  means  of  micro- 


266  Experimental  Wireless  Stations. 

phones  in  cascade  is  explained  in  patent  1,163,180. 
Patent  1,127,371  shows  how  an  audion  may  be  used 
in  connection  with  a  relay  circuit  for  wireless  control 
purposes.  Patent  1,165 >412  shows  a  practical  installa- 
tion of  a  wireless  set  on  an  aeroplane,  but  employs 
the  objectionable  hanging  wire  antenna. 

AERIALS  RECOMMENDED  FOR  VARIOUS 

WAVELENGTHS. 

The  following  dimensions  are  suitable  for  four- 
wire  aerials  of  the  "L"  type  with  spacing  between 
wires  not  less  than  0.02  of  the  length.  The  length 
here  means  only  the  flat  top  length,  as  the  lead-in 
length  will  vary  with  the  location  of  the  set.  To  find 
the  amount  of  wire  needed  multiply  the  length  of  the 
aerial  and  lead-in  by  four,  which  gives  the  number 
of  feet  required.  As  regards  range  in  miles  which 
such  an  aerial  can  in  each  case  cover,  it  should  be 
understood  that  the  size  is  no  limit  in  this  respect. 
The  values  given  are  the  approximate  natural  wave- 
lengths in  meters  and  can  be  increased  by  loading 
with  inductance  or  decreased  by  means  of  a  condenser 
in  series. 

Meters.          Height  above  ground — feet.          Length  in  feet. 

ISO  30  75 

200  50  80 

200  60  50 

200  30  90 

250  40  loo 

300  60  ioo 

400  80  130 

500  60  180 

600  80  230 

For  long  wavelengths  see  page  247.  The  second 
200  meter  aerial  is  recommended  for  amateur  trans- 
mitting. 


Supplement.  267 


Wavelength  of  Any  Aerial. 

This  is  best  found  with  a  wavemeter,  but  may  be 
roughly  calculated  from — 

L 

W=  (V+4)  4-2,  where  W  is  the  wavelength  in 
meters,  V  the  height  of  the  flat  top  in  feet,  and  'L 
the  length  of  the  four-wire  aerial  in  feet. 

WHEN  THE  WIRELESS  SET  REFUSES  TO 
WORK. 

Probably  a  majority  of  the  difficulties  arise  from 
a  misconception  or  ignorance  of  the  fundamental 
principles  involved;  for  example,  (i)  the  use  of  a  sin- 
gle wire  for  a  lead-in  from  an  aerial  composed  of 
six  such  wires,  (2)  the  use  of  too  small  or  too  large 
a  condenser  for  the  transmitting  circuit,  (3)  faulty 
insulation  or  design  of  instrument,  such  as  using  a 
helix  or  oscillation  transformer  for  a  %  kilowatt  set 
which  has  No.  14  wire  for  its  primary. 

"I  get  a  good  spark,  but  cannot  radiate  any  en- 
ergy." Probable  causes  are  a  broken  conductor  in  the 
aerial  circuit,  an  overheated  gap,  too  short  or  too  long 
a  gap,  poor  or  practically  no  ground  connection, 
enormous  resistance  due  to  loose  contact,  a  broken 
wire,  dry  earth  connection,  a  broken  condenser  plate, 
punctured  insulation,  too  much  or  too  little  primary 
or  secondary  inductance  or  both,  causing  a  lack  of 
resonance,  a  broken  aerial  insulator,  grounded  lead-in 
wire,  coupling  too  loose,  or  again,  the  values  of  ca- 
pacity, inductance,  frequency,  voltage  or  resistance 
may  be  such  as  to  prevent  free  radiation.  Occasionally 


268  Experimental  Wireless  Stations. 

an  aerial  will  really  radiate,  the  apparent  failure  being 
due  to  a  burned  out  hot  wire  ammeter,  which  is  used 
as  an  indicator.  The  proper  relation  of  the  values  for 
capacity,  inductance,  resistance,  voltage,  amperage, 
frequency,  and  the  coupling  used  are  fundamental 
and  any  variation  will  cause  some  degree  of  loss  or 
failure.  Total  failure  is  generally  due  to  a  definite 
leakage  caused  by  a  breakdown  in  the  circuits. 

"I  am  using  one  kilowatt  of  power,  but  cannot 
reach  a  friend  fifteen  miles  away."  The  cause  may  be 
one  already  given,  but  in  a  case  in  mind  the  difficulty 
was  due  to  the  use  of  too  small  an  aerial,  a  poor 
ground  and  very  poor  tuning. 

"I  cannot  get  a  good  spark  discharge."  This  is 
often  due  to  the  use  of  too  small  electrodes,  too  much 
power  for  the  size  of  the  gap,  lack  of  cooling,  too 
short  a  gap,  a  leaking  or  broken  condenser ;  or  again, 
it  may  be  due  to  the  use  of  long  connecting  wires  of 
small  cross  section,  such  as  were  found  in  one  par- 
ticular case  where  the  connecting  wires  were  heated 
hot. 

"I  cannot  get  my  set  down  to  200  meters  and 
radiate  enough  energy  to  affect  my  hot  wire  me- 
ter." A  variety  of  causes  may  include  the  use  of  too 
large  a  condenser,  an  inductance  consisting  of  a  coil 
of  too  great  diameter,  a  poor  design  of  oscillation 
transformer,  too  long  wires  for  connections,  loose 
contacts  of  the  clips,  or  connecting  wires  of  too  small 
a  cross  section.  In  many  cases,  an  inductance  coil 
of  the  cylinder  type  will  give  better  results  with  a 
smaller  diameter,  say  six  inches  or  less,  and  a  large 
conductor,  say  No.  o  to  4,  than  is  ordinarily  used. 
The  aim  should  be  to  use  a  condenser  and  inductance 


Supplement.  269 


which  will  allow  at  least  one  complete  turn  of  the 
inductance  to  be  included  in  the  primary  200  meter 
circuit.  A  pancake  type  of  oscillation  transformer 
embodying  this  principle  of  small  diameter  and  large 
conducting  surface  is  also  suitable. 

"I  can  hear  NAX  clearly,  why  cannot  I  get  Ar- 
lington?" The  usual  reason  for  this  is  that  a  small 
station  has  insufficient  wire  in  use  to  attain  the  neces- 
sary high  wave  length.  It  is  a  simple  matter  to  con- 
struct a  large  loading  coil,  with  taps,  to  bring  a  small 
set  up  to  the  longest  wave  length  now  in  general  use. 

"A  station  150  miles  from  here  formerly  came  in 
very  strong,  but  now  I  can  hardly  hear  it."  It  was 
found  that  the  station  mentioned  had  changed  its 
wave  length,  but  the  cause  might  have  been  poor  con- 
tact of  the  sliders  or  coupler  switches  or  a  non-sensi- 
tive detector.  Often,  after  some  months,  a  conductor 
used  in  the  circuits  will  become  grounded  or  broken. 

"My  set  tests  out  fine  with  a  buzzer,  but  I  cannot 
get  even  static."  This  failure  is  due  to  a  poor  ground 
or  no  ground,  or  a  grounded  aerial,  or  a  broken 
lead-in,  or  a  broken  wire  in  the  primary  inductance 
(usually  near  the  binding  posts),  or  it  may  be  merely 
a  case  requiring  intelligent  tuning. 

"I  am  operating  a  ship  station  using  a  motor 
generator  set,  but  I  have  to  connect  a  battery  across 
the  fields  to  get  the  generator  started."  This  often 
happens  with  small  generators  because  of  a  loss  of 
magnetism  due  to  a  variety  of  causes,  such  as  faulty 
connection,  the  iron  used  in  construction,  etc.  A  few 
dry  cells  are  generally  sufficient  to  supply  the  starting 
energizing  current,  after  which  the  fields  build  up 
rapidly. 


INDEX  TO  BOOK  AND 
SUPPLEMENT. 


[Numbers  refer  to  pages] 


c. 


Preface,  4. 

Aerials,  18;  balancing,  230; 
construction,  30-38;  di- 
rective, 26;  duplex,  23; 
flat  top,  27;  ground,  21, 
231;  invisible,  20;  L,  27; 
length  of,  23;  looped,  28; 
long  wave  length,  248; 
purpose  of,  12;  spacing 
wires  of,  24;  supports 
for,  20,  34.  Various  wave- 
lengths, sizes  for,  266. 

Aerial  umbrella,  25. 

Aerial  switch,  99. 

Aeroplane   wireless,  226. 

Amplifier,  234,  245. 

Antenna.     (See  Aerials.) 

Antenna  circuit,  79- 

Armstrong  audion  circuit, 
241. 

Arc  oscillator,  146. 

Atmospheric  disturbances, 
1 6. 

Audibility,  of  human  ear, 
172. 

Audibility  meter,   180. 

Audion,  233;  principle  oi, 
operation,  236;  effect  of 
magnet  on,  238;  genera- 
tor of  undamped  waves, 
240;  amplifier,  244;  with 
crystal  detector,  245. 

Automobile  wireless,  226. 

B. 


Capacity,  50;  calculation  of 
condenser,  105;  for  trans- 
mitter, 73;  series  and  par- 
allel connections,  115. 

Cascade  amplifier,  234. 

Cascade  receiving  circuits, 
243. 

Codes,  wireless,  219. 

Crystal  detectors,   162. 

Condensers,  construction  of 
transmitting,  109;  con- 
struction of  receiving, 
195;  how  charged,  104; 
size  of,  105;  transmit- 
ting, 103;  variable,  198. 

Continuous  waves,  produc- 
tion of,  145. 

D. 

Damping,  65. 

Dead  ends,  250. 

Dielectric  constants,   106. 

Differential   tuning,   192. 

Directive  aerial,  26. 

Direction  finder,  227. 

Duplex  stations,  231. 

Detectors,  231;  adjustment 
of,  170;  comparison  of, 
244;  construction  of,  165; 
function  of,  158;  min- 
erals for,  162;  operation 
of,  161;  sensitivity  of, 
160;  types  of,  161. 

E. 


Beaufort  scale,  255. 

Break-in  systems,  101. 

Bridge      receiving      circuit,       Einthoven     galvanometer, 

188.  173. 

Buzzer  test,  171.  Electrolytic  interrupter,  93. 


Index. 


271 


Electromagnetic  waves,  ve- 

locity of,  18. 
Experimenters'   rights,   214. 

F. 

Fleming  valve,  232. 
Frequency,     effect     on     ca- 
pacity, 73- 

G. 

Goldschmidt  generator,  155. 
Grounds,  39. 
Ground  aerials,  231. 

H. 

Helix,  construction  of,  119. 
Heterodyne   receiver,   229. 
High   frequency,   67,    155. 
Hot     wire     ammeter,     135; 
construction  of,  138. 


I. 


Inductance,   51;    calculation 

of,  1  1  6. 
Insulators,  28. 
Intensity  of  signals,   meas- 

uring,  180. 
Interference,  15,  182. 
Interference  prevention,  180, 

181,  192,  212,  229. 

K. 

Keys  for  transmitting,  97. 
Kickback  prevention,  95. 
Korda  air  condenser,   196. 


Lead-in,  30,  35. 
Lepel  Arc  System,   149. 
License,  obtaining  a,  216. 
Lieben-Reisz  amplifier,  234. 
Lightning     protection,     39, 

42. 

Loading  coil,   124,   191. 
Long  wave  length  stations, 

247. 


Long  wave  receiver,  242. 

Loop  aerial,  192. 

Loose-coupler,  189;  c  o  n- 
struction  of,  208;  for  long 
wave  reception,  250. 

M. 

Magnetic   blowout,   98. 
Measuring  instruments,  133. 
Mutual   inductance,   118. 

O. 

Oil  key,  97. 

Oscillations    explained,    47; 

production    of    sustained, 

145-155. 
Oscillation  transformer,  121. 

P. 

Patents,  216;   complete   list 

of  U.   S.,  256;   discussion 

of  recent,  264. 
Pliotron,  234. 
Plural  receiving  sets,  252. 
Poles  for  aerial,  36. 
Protective   devices,  42,  95. 
Quenched    gap,    adjustable, 

155. 

Quenched  spark  gap,  151. 
Quenched     spark     system, 

153. 


Radiant  energy,    17. 

Radiation,  determining  best, 
139- 

Radiation  resistance,  231. 

Radio-communication,  ten- 
dency of,  217. 

Railroad   wireless,   226. 

Range  of  transmission,  68. 

Reactance  for  transformer, 
70. 

Reactance  coil  construction, 
89- 

Receiver,  tuning  a,   185. 


272 


Index. 


Receiving,  long  undamped 
wave  set,  242;  process  of, 
159. 

Receiving  condensers,  191. 

Receiving,  long  waves,  aer- 
ial for,  248;  tuner  for,  249. 

Receiving  stations,  156;  cir- 
cuit for,  187;  how  it  op- 
erates, 179. 

Resistance,  59. 

Resonance,  52;  harmonic 
effect,  57. 

Rotary  spark  gap,  128. 

S. 

Series  spark  gap,  127. 
Shunt  resonator,  141. 
Singing  arc,   149. 
Spark   coils,   capacities   for, 

74;  data  for,  91. 
Spark  gap,  78;  construction, 

126;    in    compressed    gas, 

132;  purpose  of,   125. 
Spark  rate,   high   desirable, 

132. 
Stations,     possibilities     of, 

213. 

T. 

Telemechanics,  230. 

Telephone  receivers,  157; 
construction,  176-178. 

Theory   of  transmission,  8. 

Thermionic  tubes,  opera- 
tion of,  237. 

Three  slide  tuner,  188. 

Ticker,   175. 

Time  signals,  252. 

Transformers,  81;  construc- 
tion, 84;  dimensions  of, 
83;  magnetic  leakage,  84; 
types  of,  69. 


Transmission,  effect  of  day 
and  night  on,  14. 

Transmitter,  46;  character- 
istics of,  63,  64;  power  of, 
72. 

Tuned  waves,  16. 

Tuner,  construction  of,  204. 

Tuning,  49;  accurate,  60; 
devices  for,  202;  good 
and  bad,  62;  methods, 
185;  process  of,  with 
loose  coupler,  189;  trans- 
mitter, 58. 

U. 

Ultra-audion  receiver,  239. 
Undamped  waves,  65;  au- 

dion    generator    of,    240; 

receiving  set  for,  175,  242. 
Universal  detector,  166. 

V. 

Vacuum   valves,   231. 
Variometer,  207. 

W. 

Wave  length,  19,  20;  calcu- 
lation, 75;  determining, 
134;  limitation  of,  56. 

Wave  meter,  134. 

Wave  transmission,  10. 

Weather  code,  255. 

Weather  reports,  253. 

Wireless  compass,  227. 

Wireless  law,  215. 

Wireless  telephone,  146,  246. 

Wireless  troubles,  remedies 
for,  268. 





14  DAY  USE 

RETURN  TO  DESK  FROM  WHICH  BORROWED 

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FEB2    197525 

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